Not sure if they have demos for the ones that i name but these are some that i like
Halo ( u prooly have that)
Call of Duty 2
F.E.A.R ( dont have it but heard it was very good)
Counter Strike ( dont think there is a demo)
Half life 2
- Quite possibly the most fun singleplayer game I have EVER played. The multiplayer is EXTREMLY fast paced. You'll love it. It's kind of a combination of a fighting game and an FPS.
- This game is the game by which generally most other FPS are judged by. It blends the element of the FPS with an element of combat and an MMO (Massive Multiplayer Online) game. It's horribly addicting and freakishly fun. Definetly a must-have.
Counter-Strike Source/Coundition Zero/1.6
- This is the game that really sparked the FPS genre. Get this. It's addicting, fun, and amazing graphics.
Call of Duty 2
- Amazing graphics! Very fun in a LAN game. Although I find that the way damage is dealt with in the game is poorly constructed, but generally the same thign can be applied to nearly all games. However, this game is hard to play most of the time because you aren't given a crosshair unless you aren't moving, which makes it difficult to play at times. Although I recommend it to a certain degree.
- Haven't played much of this game except for once, and, it was fun. Get this.
hm, i have to say F.E.A.R. should be one to check out. it has really great action and the best slowmo effects i have seen, though it kinda lacks in creativity. There is only about 4 bad guys you fight, all look the same, level design is great. A bit short though. Doom 3 is good, not the best. REally great graphics engine but not very fast paced. Counter-Stike source is probably the FPS i play most, really good, but only fun for multiplayer becuase it's aimed towards online play. Half life 2 is one you should really get, though a bit outdated it still one of the best single player experiences i had. HALO is a pretty strong on single player campaign as well as multiplayer. hope i helped.
Far Cry is incredible. At around 15 bucks, it is a MUST have. I can't believe more people don't know anything about it, but it deserves a lot more attention than it receives. Excellent single-player which I'm still not done with (and I've had it for a while) and I haven't even had time to try the multiplayer.