Have you tried any of the Splinter Cell, Ghost Recon, or Rainbow Six games (you can tell who my favorite person is)? I just finished Choas Theory and LOVED it. I have beaten the original and Pandora Tomorrow and liked both of those too. I am getting Double Agent soon for the 360 and am looking forward to that. I have played Ghost Recon for awile and also really enjoyed that series, but I prefer Vegas 2. For FPS, these are my favorite.
If you want to try strategy, I probably have 800+ hours in Civilazation 4 and would reccomend that game in a hearbeat. Another strategy game I like is CnC 3 and Kane's Wrath expansion. I grew up playing Command and Conquer and really like the whole series. Company of Heroes is another great game.
Lastly, I think you should definitely play KOTOR, Oblivion, and Morrowind. These are my all-time favorite RPG's. I know it might be kind of weird, but I liked Morrowind more than Oblivion. There both awesome, but Morrowind just felt more like a role playing game. When you leveled up, you not only saw improvements in combat, but also in normal things like trying to get from place to place. I remember being so proud when I could run from Vivec to Balmora without stopping, whereas in the begining I could barely make it from Seyda Neen to Balmora. I also despise fast traveling in Oblivion. It really detracted from the game for me.
I would reccoment any of these games for you to play. As a bonus, most are old enough that you can get them pretty cheap.