No FPS game can even rival the greatness of Tribes 2. Greatest FPS game ever... And its FREE???
One the beautiful things about Tribes 2 is how many levels of gameplay are going on at once for you. The simply act of your moving around, alone, can come close to the complexity of many other FPS's. With their skiing and jet pack system, you are constantly having to be aware of your jetpack energy and always be watching the terrain the you gracefully ski upon.
As for the weapon system, while in most games you simply aim your crosshair at the enemies head and start shooting, in Tribes your weapons have projectile speeds, meaning you're going to have to be constantly judging the enemy's motion and deciding how far ahead to shoot. These offer some VERY rewarding hits on the other players.
It is very team oriented. It is much more similar to sports teams than FPS's in the sense that different players will have very different and unique experiences and tasks. The skills, the armor you use, the weapons, the playstyle you use when defending a flag are not even close to what you'd be using in capturing the enemies flag. This allows for specialization among players which offers an even more rewarding team experience.
I am just SHOCKED at how little current games have taken from the game play of Tribes. I imagine that it may have to do with the difficulty of this game. Unlike other FPS's, you will not just turn on this game and start getting lucky kills, it takes a lot of practice, but it is so worth it!!!!
Note: Other great thing about it.... It's FREE!! Previously the master server had been shut down after its 7 years, but earlier this year tribesnext.com launched their own. There are still many people to play with if you're interested. You just download the game from their site, and the patch and start playing!!