GTA III - PC
For the open ended, non linear gameplay and the awesome mods. I mean where else could you throw grenades at starbucks (shame it didn't do anything!). And go Vigilante hehe...
Halo - Xbox
One of the best FPS for a long time. Can't have thousands of weapons, and the little tiny touches (such as Marines punchin' the air and swearing) and atmosphere were superb. Also like the fact they didn't try to personalise the main character too much, just called him a general name. Story lines are cool but when I name my character I don't want all the cut scenes to call him alex (or whatever) /rant over
Spy Hunter - Classic
Oldie but goodie, still love playing it on shockwave. Just thought it was fun!