Don't berate me if my opinion isn't in line with yours :P
To qualify for this list it has to be made after November 2005. It's also completely my opinion and it only involves gamse I've played from beginning to end or just played extensively.
10. Left 4 Dead
Left 4 Dead suceeds on so many levels. For one it's one of the best co-op shooters out there and it's an absolute blast to play with a group or even just one friend. Sadly it's lack of content though keep it down on my list but it'll still go down as one of the better first person shooters this generation. Left 4 Dead is an example of what a co-op shooter should try to do.
Shooters this unique don't come around very often. Bioshock is a rare breed of shooter. For one it ignores online which has become a standard in shooters. It also features many gameplay elements not standard in shooters. Plasmids also keep the game feeling fresh by giving the player what basically amounts to 'superpowers'. This game also tells one of the best stories from any first person shooter and for that reason it earns a respectable spot on this list.
8. Gears of War 2
Gears of War is every thirteen year old's wet dream. It's a bunch of muscular guys chainsawing alien scum on a distant planet. It's an immensely satisfying game and when compared to the first, it almost renders it obselete. This game is gorgeous, it tells a pretty decent story, and it plays like a stellar action movie. The online component is a lot of fun but sadly it is bogged down with some issues. Horde mode though will always be a blast and the co-op is as good as ever. Gears of War earns number 8 for all these reasons.
Crysis is not only visually stunning. It's also pretty fun as an open ended sandbox-esque shooter. It has decent AI but it suceeds on keeping the action open ended and varied. Though the alien sector aren't as fun you'll forgive it. The online is decent though it could have used some work but overall Crysis is a great game well worth checking out. It's a true testament to the power of the PC.
6. Half Life 2: Episode 2
Episode 2 took everything from Episode 1 and Half Life 2 and expanded on it. It made the good better and it learned from all past mistakes of the series. It also gave the best story thus far in the series and it's given great setup to Episode 3. I strongly believe it is the best single player only first person shooting experience this generation.
5. Resistance 2
Epic doesn't begin to describe this game. Much improved over the original, Resistance 2 delivers on everything it promised. Co-op is an absolute blast and the online component is some of the best on consoles. It's just an all around steller game that I greatly enjoyed. It's one of the reasons I am bound to purchase a PS3.
4. Battlefield: Bad Company
As a die-hard Battlefield fan I didn't think I'd enjoy Bad Company much; in the end though it surpassed my highest expectations tenfold. The game is excellent and though it lacks many standards like co-op, deathmatch, and team deathmatch, what you do get is so much fun it's unbelievable. The single player is light and fun. It's never too serious and it knows what it's meant to be. Blowing stuff up is just unbelieveable and the online is just excellent. With one of the best communities out there the teamwork aspect is just top notch. I loved it and I can't recommend it enough.
3. Team Fortress 2
No game was more robbed by Gamespot's editorial team then Team Fortress 2. As I've stated before this game is the perfect online team-based game. Working together is necessary and because of the games stellar community it just works. The game has some of the best developer support on the PC and it's an absolute blast to play. Few games are as fun and satisfying as Team Fortress 2 and it's one of the few games this generation I'd call near flawless.
2. Halo 3
If any game deserves a medal it's Halo 3. Halo 3 does so much it's insane and mind boggling. The campaign though slightly weak is excellent and it's a suitable end to the series. It's given a large boost though by it's stellar co-op which is a ton of fun. The online component is an example of perfection. With so many modes to choose from it's almost endlessly replayable and with Bungie's constant support shows that Halo 3 will be around for a long time to come. People shouldn't hate on Halo, I used to hate on it and I paid the price. This game is popular for a reason.
1. Call of Duty 4: Modern Warfare
I spent a lot of time thinking about what the number 1 should be. Choosing between Halo 3 and Call of Duty 4 is like choosing your favorite child. Both games have given me so much. In the end though I had to go with Call of Duty 4. The single player is one of the best experiences I've ever had. Though short, the character development, story progression, and general structure is second to none. The story was genuinly shocking and it had me on the edge of my seat. It's not predictable in the least. Though is misses out on co-op, it's online is excellent. You can either choose to play the online as a 'lone soldier' or you can try your hand in team based modes. Because of the game's open ended online options it's just never ending and it's one of those things that is hard to get tired of. Call of Duty 4 is Infinity Ward's magnum opus and I can't wait to see what they have in store for Modern Warfare 2.