Fenixp: Well, since I agree with the most and am currently bored a bit, I'm going to supplement you there:
XIII - Basically, it's cartoony goodness with serious balance issues and great + well told story. If you value story in your shooters, do get this, but also keep in mind that you'll have to get trough quite a few annoying stealth passages and that you'll hit some difficulty spikes. Other than that, this game is truly fantastic, from it's style to it's mechanics. Just so we're clear as to how awesome it is: When you score a good hit,
this happens. You get 3 comic-like frames detailing your opponent's death. Damn satisfying. And I'm not even mentioning that most sounds are accompanied by on-screen text like 'KABOOM!'
Chaser - Chaser is good for one thing: It's length. It's really, really long, it's got plenty of weapons, and gets quite variable as well. However, while different areas are really varied, the level themselves are not. When you enter an area, you often just walk trough the pretty much same corridor until you get to the next level. Also there are some collision detection issues where you can't go trough 2mm high rubble on the floor, and enemies instantly react to your presence and are 100% accurate, which is annoying. 4/10, would not bang.
Tom Clancy's Ghost Recon - Now this one is a treat. Tactical military shooter. It's not as realistic as, say, ArmA: Cold War Crisis, but it sure has it's moments. You play as one of the guys from tactical unit, deployed for specific tasks - and it's up to you how do you decide to aproach them. Maps are usually quite big and open, you can pick loadout and soldiers before every mission, and when you're in-mission, you can give orders to your guys and your 'direct control' between them - so, at one moment you can be sniper, at another you can switch to your heavy weapon specialist and spray enemies with bullets.
Missions are quite diverse, game's not exactly easy since one hit usually means that you die, and it requires some tactical thinking on your part. I do recommend this one, but only if you have already played IMO superior ArmA: Cold war assault.
Unreal 2 - it tried to repeat success of the first game. It failed. While it's not actually a bad game, it's just not very interesting - it's quite a bland sci-fi shooter with some nice ideas (deployable turrets) and crazy difficulty curve. You won't actually miss anything if you just skip this one, really.
I can´t understand why you inlude Unreal 2 on the list then... Or you´re just talking about the ones you played?