Like I said before, I'm giving it to Grim Fandango.
I can appreciate OoT, RE2, H-L, Fallout 2 and BG, even if I feel all of those are overrated.
Unreal was a step towards Halo.
A favorite of mine is Carmageddon II: Carpocalypse Now, may have to say it's better than the first.
Colin McRae Rally started the whole great series. R4: Ridge Racer Type 4 is another of my favorite driving games.
Also worth mentioning: Tom Clancy's Rainbow Six and Soulcalibur.