My favorite FPS game has been Serious Sam, the original. I liked Unreal Tournament, but Quake 3 was too fast for me. Quake 1 and 2 were good too. The last FPS game I've tried was Serious Sam : the Secound Encounter, but I've never ben able to finish the third level (the antigravity chamber was beyond my limited skills).
If you ever have a chance with some free time (I know you're busy), maybe give the game Portal a chance. It's more of a fun puzzle game with interesting twists. It's not nearly as fast-paced as UT or serious sam, but worth trying.
I enjoyed serious sam for lan parties but it never held my attention for a single player game.