Comparison of free software shooters
There have been many free software first-person shooters (FPS) projects  over the years, from modded Doom and Quake engines to enhance the  existing games (ezQuake, EGL,  ZDoom),  to free art packs such as OpenQuartz or OpenArena.   In 2002, along came Cube, a single and  multiplayer FPS based on its own engine, including artwork, maps, models  and an ingame map editor. In the freeware (and Linux compatible!) world  a little-known game called Legends, a Tribes-inspired game, appeared  yet remained closed-source. Filling the FPS gap in the open-source world  has usually been left up to commercial companies who release their  games with Linux support (i.e. Doom3, Unreal Tournament 2004, Loki  Software's work) or freeware games produced by commercial studios(i.e.  America's Army, Wolfenstein: Enemy Territory) or simply running Windows  games run via wine. In the last few years a few built-from-scratch  community-based FPS projects, most built on the GPLed Quake engines,  have popped up, among them are Tremulous, Alien Arena, Nexuiz, and War§ow.  Some have kept their art assets under a closed license (War§ow), while  others have also released their art under an OSS license (Nexuiz). 
 For this comparison, we'll take a look at active, robust and  community-developed free software shooters. Most released free software  shooters are designed for multiplayer, a logical step for a game  developed in an online community, however most also feature a bot-based  single-player mode.This feature seeks to be a little more thorough and go a step further,  ranking the following seven games: Alien Arena, Nexuiz, OpenArena,  Sauerbraten, Tremulous,  War§ow,  and World of Padman. In ranking  these games, gameplay, design, innovation and presentation (in that  order) will be held as primary criteria.

1. War§ow
  War§ow is a deathmatch shooter with a  focus on freedom of movement, attracting new players and fostering a  competitive scene. It is built on Qfusion, a heavy  modification of the GPL Quake 2 engine. From the user interface, to the  gameplay, to even the netcode the game feels more like an improvement on  Quake 3 than anything, stretching far beyond the original Quake 2  engine. Along with World of Padman, wSw stands out in this comparison by  actually using colorful and clean graphics as opposed to Quake-inspired  dark visuals. Warsow manages set itself even further by using  cel-shading to create very clean, yet stunning visuals which regrettably  can strain slower systems. In addition, the maps all feature a unique  visual style that varies between maps yet retains the clean and  cyberpunk visual themes.While sticking to basic deathmatch gamemodes,  wSw manages to refine them and remain fun and enjoyable. Weapons are  generally the same as Quake 3 and 4, although with a more polished feel.  wSw however, implements a dual tier system for ammos. Weapons have weak  and strong ammos which add more functionality to the gameplay while  still keeping the basics simple. War§ow’s main change on top of basic  Quake 3 gameplay is an expansion of movement options, featuring  strafejumping and bunnyhopping from Quake along with dash, walljumping  and aircontrol. Polish and high quality standards are what make War§ow  the free software FPS to beat. All aspects, from movement to maps to the  gamemodes, seem refined and balanced. It was not until the mid-2007  release of the 0.3x version (currently 0.32) that wSw became refined  enough to set itself apart from the others mentioned here. While many of  the previously mentioned games have good original ideas and interesting  features, they do not present games that match the quality of  commercial offerings. In terms of multiplayer features and  customizability, War§ow matches and outclasses any released commercial  deathmatch game. Many of the other games seem to fall into the common  trend in free software projects: lots of great ideas without friendly  and useful implementation, while War§ow is in the style of Firefox,  polished and accessible.  Maps seem to have serious consideration for  item placement and flow, voice-overs seem clean and crisp,  lag-compensating network code keeps online play smooth. While many games  seem to concentrate in only one area, Warsow seems to do well in almost  every area. teamplay, 1v1, new players and experienced players all have  been considered in design. Out of the previously mentioned games War§ow  also has the largest community with over 250 servers. Competitive  gaming is a key part of wSw and there exists a very large competitive  community, for example, an international LAN competition was hosted in  2007. Competition drives many of the design decisions behind the game,  and always leaves players with something to do and strive for. This also  leads to the game's largest flaw, a steep learning curve that pushes  wSw beyond the scope of many casual gamers; although the newly added  Clan Arena mode lets new players have a simple gamemode where they can  stand a bit more of a chance. wSw thrives on bunnyhopping and strafing  skills which take time to develop, tutorial videos exist but lack of an  ingame tutorial seriously limits adoption. The high quality art  direction, the implementation of some simple yet effective original  ideas, combined with the refined Quake gameplay leaves War§ow the  champion of the pack for free software shooters. Warsow was able to do  what many free software projects strive for, take an established  concept, clearly implement additional original ideas, refine the core of  the project, and then present it in a very professional way.
2. Tremulous

Tremulous sets itself aside from all of the previous games in that it  isn’t a FFA deathmatch game. Instead Tremulous is a team-based game with  aliens vs. humans where each team constructs a base and players are  given the ability to obtain individual upgrades. With a kill-based point  system, Tremulous rewards combat, allowing players to get better  equipment so they can better attack the opponents. The two teams are  unique and the concept and style of the game is rather original. If  anything, Tremulous can be related to the Half-Life mod Natural  Selection, although without the RTS commander mode. Tremulous has had a  very constant release cycle with the latest 1.1 being released about a  year ago and the community and development remaining active. The game is  based on the Quake 3 engine, and although there are only 8 maps,  they’re all varied, unique and high-quality. The only notable flaw was  that the options menu didn’t show up until the player joined a game.  Tremulous has rich gameplay but still very accessible to new players,  featuring onscreen help and tips while you play. To further the point,  Tremulous comes with a descriptive and friendly manual for those who  want to learn the details of the gameplay. The game is simply fun; there  is just action for those who want a simple game and tons of features  and detail for those that want a bit more. The graphic design is  consistent, dark and sci-fi futuristic with a bit of variance but a lot  of consistency. The game has a large following as far as free software  goes with a about 200 servers and at least a couple games any time of  day. The performance is clean and consistent and it looks as good as  Quake 3 generation mods. Tremulous is one of the few free software  projects to combine an original idea with a polished implementation and  good direction. The few maps and one gamemode really keep the style  focused and clean. Tremulous could use more maps, more variety, more  content and perhaps more robust gameplay, but 1.1 is a great release and  future versions are definitely something to watch out for.
3. World of Padman

World of Padman originated as a modification on top of Quake 3 in 2004.  With the release of GPL licensed Quake3 code, World of Padman was  released as a stand-alone game on top of ioquake3. From that  perspective, World of Padman was designed more in the style of the mod  community (art-driven projects) than that of the free software community  (code-driven projects) but nonetheless, its free software now. The game  is based on a comic book and has unique colorful graphics with clear  comic inspiration. World of Padman gameplay is very similar to that of  Quake3, a little bit different, a little refreshing, but nothing too  strikingly new. Killing other players is satisfying and just silly fun.  If anything, World of Padman is proof that deathmatch gaming doesn’t  need to be blood-covered, violent and serious; it can be silly, cutesy  and fun. World of Padman features several maps, each quite unique and  but fitting with a common style. For example, players are characters  about 3cm high and fight in real rooms like a bedroom, library, kitchen,  etc. It’s not a new approach for maps, but it definitely is fun and  interesting; combined with World of Padman’s art direction, this leaves  for rather refreshing arenas. And while maps like this sure are great  free-for-all fun, they aren’t really designed for competitive play,  limiting potential for a hardcore community (the driving force of many  shooter games). Gameplay is similar to Quake3 with slower rockets and a  very satisfying machine gun being the most notable differences. It has a  small community at about 26 servers but the large installer above 500MB  might be slowing adoption. The game is very polished , it has several  gamemodes (including a unique “Spray your Color” mode) but gameplay  still boils down the basic Quake-like fragging. While World of Padman is  not, by any stretch of the imagination, a bad game, it lacks the  innovative gameplay design goals of several of the games features here,  it feels like Quake with polish and restructured objectives. While the  game has great style rivaling the stylistic nature of any commercial  game, it lacks advanced graphical features of Nexuiz & Sauerbraten  or unique gameplay features of Nexuiz & Alien Arena. If you want to  see what the gothic Quake 3 would look like if it were designed by  color-loving comic artists with a sense of humor and a sense of fun  style, World of Padman is exactly what you’re looking for but  regrettably that’s about as far is it goes at the moment.
4. Nexuiz
  Nexuiz is another game that follows the  fast, dark, and intense free-for-all deathmatch style first set down by  Quake 1 in 1996. Nexuiz curiously enough is built on the Darkplaces engine, an  expanded version of the GPL released Quake 1 source. While the basic  graphics are seem to be up to Quake 3 standards, expanded lighting  options allow the graphical features to be brought up to just below  Quake 4 standards. Although the newest version still follows that simple  deathmatch style, the fast, varied maps and lots of explosive action  with interesting two fire-mode weapons leads to gameplay that is about  as intense as it gets for shooters. Good sound combined with varied and  unique weapons attests to the polish that has gone into bringing Nexuiz  up to version 2.3. Nexuiz has lots of maps which seem to be slightly  varied in style, but still are predominantly covered with dark  overtones. While most of the game is cleaned up far beyond its Quake 1  roots, it is still lacking in presentation with the menu being very  circa 1990s. The community is strong and with about 80 servers, and  finding a game is fairly easy. Nexuiz has lots of content, style and  features and is very well done for a FFA game but some areas could use  some more work and showcasing of its unique features and modes.
5. Alien Arena  Alien Arena is a Quake 2  based deathmatch game that tries to draw on a conflict between humans  and aliens. However this distinction between two player types rarely  stretches beyond player models. The latest release, Alien Arena 2007  6.10, still has many visual characteristics that appear outdated and  reminiscent of Quake 2. Although there are game modes such as deathball,  CTF, and assult, with a dark artistic style, fast gameplay with strong  weapons, Alien Arena is predominantly a deathmatch game.  The original  game modes aren’t very well presented and seem to be underutilized,  which is a shame because they seem to be fairly innovative. For example,  Alien Arena includes vehicles in certain game modes, but the feature is  hidden away on a few rarely-played and rarely-promoted maps.  Although  the external server browser and main menu are very nice, much of Alien  Arena seems to be muddled and lacking polished design. The HUD lacks  many critical features like a weaponlist or a clock, and the icons and  graphics are not clear. Alien Arena lacks many obvious gameplay features  that have become standard in modern games, like removing the quad  powerup for the duel gamemode. While many of the weapons seem to be  recreations of weapons in Unreal and Quake, the two fire modes for each  weapon adds interesting diversity on top of Quake-inspired gameplay  rules. But overpowered nature of the weapons, especially the chaingun,  leaves much to be desired from the gameplay. The community isn’t very  large at about 60 servers, but the game seems to be a bit lacking in  clean presentation so it may not be as attractive to new players. Alien  Arena seems to be working with lots of new and interesting original  concepts but still needs work to match the artistic and gameplay quality  of the other games covered here. If the project were to shift gears and  focus a bit more on polish, design and presentation instead of creating  tons of content (which it already has lots of), it has the potential to  move beyond "dark FFA deathmatch action" and really be something quite  original and remarkable.
6. OpenArena
 
 OpenArena is a project to  create GPL-licensed art assets on top of the open-sourced Quake 3  engine. It uses the latest snapshot of the ioquake3  engine and a mix of GPL assets ranging from original work to resources  from Nexuiz, Cube and others. OpenArena 0.71 is a fairly large release  at over 200MB. Most of the space is spent on many maps and models, some  of which are regrettably lacking in quality. Some are straight  recompiles of the GPL released Quake 1 maps (oa_dm1-7), which fail to  use many of the advanced lighting and detail offered in the new engine.  OpenArena seems to generally lack coherent art direction or design; most  the maps, models and artwork seems like a half-done mix of Quake 3’s  gothic architecture and anime. The gameplay stays true to what was  included in Quake3, so it can be rather enjoyable. On the other hand,  much of Quake 3 Arena's popularity came from being done in such a  simple, directed, and polished manner and OpenArena lacks much of the  polish that made Quake3 so enjoyable. However, the project is still in  its early stages and the task at hand is a rather large one. The goal of  recreating GPL Q3A artwork on top of the GPL code is both noble and a  great contribution to the community. OpenArena games still seem limited  to FFA and with about 70 servers, the community is rather small. While  Q3A gained popularity as a competitive game, the developers of OA don’t  see that as a target market so the depth of gameplay is unlikely to  expand. At the moment, most the games on this list display far better  art direction and design, which is regrettable as OpenArena is the most  art-driven and least code-driven game in the group. At the end of the  day though, OpenArena is about making a free game that has lots of  simple & fun deathmatch action a la Quake3, and that is where it  succeeds.
7. Sauerbraten
 
 Sauerbraten is basically  Cube 2, the sequel to one of the most influential free software shooters  released to date. The engine is completely reworked with brand new  graphics rendering features rivaling that of Quake4. Like Cube,  Sauerbraten has a built-in map editor that allows player to edit maps  from within the game, making this one of the friendliest games for  content-creation. The latest version of Sauerbraten, 2007-09-04, is  little more than a subversion snapshot packaged and stabilized for wider  distribution; the game is still in heavy development. Sauerbraten  gameplay drastically differ from anything Cube offered, with simple  Quake-style weapons, game effects, and the same Quake3-like FFA action.  It is worth noting that Cube (and Sauerbraten) give you a weapon when  you pick up the appropriate ammobox; there is no separation between ammo  and weapons.While it has some cool features, the game still feels like  more of a concept demo than an actual game, and with only 20-30 servers,  half running instagib, there isn’t much of a community following.  Single player is reminiscent of Quake1, with enemy monsters in a variety  of maps. The menu is actually one of the coolest I’ve seen implemented  in a game, it spawns as an object ingame and faces you, however the lack  of a main menu upon load adds to the tech-demo feel. Despite the  tech-demo nature of the game, Sauerbraten has a good soundtrack, lots of  maps, good quality models, well-done artwork and textures. The gameplay  isn’t anything astounding but with pretty decent maps and gameplay  reminiscent of Quake3, Sauerbraten definitely offers something for  people who just want some simple mindless action with some eye candy.  Sauerbraten is a really cool project, but right now it remains that, a  project of what can be done, more than a game.
source:
http://www.linux-gamers.net/smartsection.item.81/comparison-of-free-softwareshooters.html