Well GTA3 for 3d sandbox games is debatable for those that remember the classic gem Body Harvest on the N64.
Just my 2 pence on the subject as it came out earlier and ironed out the bugs int he system that allowed it to evolve into GTA series most remember.
edit: Regarding Halo for the FPS genre i believe that for all the good it did it still did a lot of harm with bots in multiplayer portions of the FPS games hardly ever being used since Halo:CE came out.... I want my PD bots back :(







