...
Metroid Prime changed the whole way people looked at FPS games, and showed that it was possible to create a huge world with different environments to revisit and stuff.
God of War recreated the whole 3D beat 'em up genre by adding an intensive storyline, and making active-time events appear more often than any other game before that (for the best, or worst). Also, let's not forget some RPG elements, such as weapon upgrades, etc.
Halo: Combat Evolved was the first ''feature-heavy'' FPS game on consoles, adding vehicles, various grenade types, co-op play, an impressive soundtrack, etc.
It's too hard to answer.
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...
