I know this game has been covered before (here: http://tigsource.com/articles/2008/06/27/teeworlds). Still, time has passed, the game had several major updates and I simply felt another review would be useful for the community.
I advise everybody to get the game now, that way it'll be installed before you finish this text. Don't worry, teeworlds is open source and works on all major operating systems.
The game can be found here: http://www.teeworlds.com/
Teeworlds is a fast-paced 2d sidescrolling multiplayer-only shooter played on a computer. The game features cartoon-themed graphics and physics, and relies heavily on classic shooter weaponry and gameplay. In the game, you roleplay a Tee, a cute ball who carries around various weaponry and a hook, allowing some Spiderman like movement. Overall, the gameplay is simply really fun. The pacing is extremely well done and the movement is pretty intuitive.
The gameplay of this independant game can, despite it's small size, compete with bigger and expensive productions in terms of fun and innovation. What sets Teeworld apart from other sidescrollers game is it's huge focus on mobility, it's innovative use of the grappling hook and it's weaponry. The instant respawn is also well implemented as it keeps you right in the action.
Now a bit of talk about the weaponry: you start the game with only a hammer and a long range pistol (and the hook), but there are other weapons lying around. On most maps they're everywhere so ammunition isn't too much of an issue. The weapons are varied and better players will learn to switch weapons quickly as they each have their own, very specific, situations. Sadly, there aren't a whole lot of weapons yet, but the ones that are implemented are simply perfect and offer different playstyles. I should mention that the next version will support more weapons and powerups.
Having weapons and clicking fast isn't everything in this game: due to the ammo being relatively slow and the liberty the grappling hook offers evading bullets can be done. In a fight between more experienced players, the Tees will usually move at a speed that makes hitting the opponent a matter of good timing and prediction. Sadly, it's pretty hard to find the better players.
One of the biggest goals of the Teeworlds crew is to make their game very casual friendly, or in other words, to attract casual gamers. According to my chronometer they did that pretty well: 15 seconds from launching the game to firing a gun (after picking a decent server). Compare that to the +20 seconds a cold launch of firefox takes (cold launch = first launch after the computer started) you can see why Teeworlds can concurrent with the casual friendly flash games.
One great part about the game hasn't been mentioned yet: the fact that there are tons of modded servers and extra gamemodes. Besides the "vanilla" gameplay in (team) deatmatch and capture the flag, you can play flagball, ninja-only, several game types that add RPG elements, instagib, freeze and the list goes on...
It keeps the gameplay varied and simply makes the game more addictive.
On the other hand, the gaming population is still pretty small (~700 online at any time) so you can't always find a server with the game mode you want. On a related note, there aren't a lot of servers on the American continent so people there should expect a higher ping (200 ms) if they can't get a server themselves. That shouldn't spoil the game though.
The graphics are well done and are easy for the eyes. Overall, they add to the fluidity of the game. The other hardware part, the sound effects are a bit dissapointing: there simply isn't any music. The sound effects are decent, but unless the map is crowded it doesn't really make up for the lack of background music.
While it can't concurrent with top games like TF2 and L4D (nor tries to), Teeworlds has it's place as a fast, fun game that is perfect for when you want to get some distraction in little time. Fans of the 2d sidescroller shooter genre should certainly try this game.
Although it's still in early development proces, it already deserves more attention and more players considering the quality of the game in this 0.5.1 version./end review
Hope I posted this in the right section and that you guys do apreciate user reviews (posting guidelines weren't very clair). To be honest, I posted this review on other sites as well, but as I'm still a bit frustrated by the lack of attention an open source title gets, I post it here as well. It's a bit long, but I did my best keeping it light and adding screenshots to break the wall of text.
Not sure about that whole "minimum number of posts to acces this forum" thingy...