TBH I don't reallylike FPS, And I really don't like multiplayer, unless it's local with friends. if it's not awesome (or have role-playing elements. i think it's boring)

1. Deus Ex
2. Half Life 2: Episode 2 (and Half Life 2) (half life 2 episode one was bleh)
3. Crysis
4. Perfect Dark
5. Bioshock
In no order
Jedi Knight II
Deus Ex 2
Half Life
Far Cry
Edit Oops: FEAR: (Boring now, fun as hell when I played it)

Really though, if it came down to just shooting mechanics I'd half to take Deus Ex, Deus Ex 2, and Bioshock.