in that case, I'll addwkrepelin said:I can't narrow it to one so I'll go with best in genre.
FPS (single player): Bioshock
FPS (coop multiplayer): Borderlands
FPS (comp multiplayer): CoD 4
TPS: Mass Effect 2
Action/Adventure: Uncharted 2
Hack n' Slash: God of War III
Platforming: Super Mario Galaxy 2
wRPG: Fallout 3
jRPG: Tales of Vesperia
Fighting: Super Street Fighter 4
Puzzle: Portal
Handheld: Dragon Quest IX
Superhero: Batman Arkham Asylum
Open World/Sandbox: Red Dead Redemption
Horror/Thriller: Dead Space
Kids/Family: LEGO Harry Potter Years 1-4
Arcade: Braid
Genre Defying: Heavy Rain
I know that's a crazy list but there is really no best game and even the titles that I've listed, all of which are superb, are still highly debatable.
EDIT: I don't play RTS, sports or music games so that's why they don't appear in the list. I also don't own a PSP so that's why the best game for the DS won for handheld by default.
RTS (PC): empire: total war
RTS (console): probably C&C3 or LOTR BFME II or supcom 2... not a lot to choose from
sports: Madden '11,MLB the show '10
i didnt really like heavy rain it didnt stand up as a game, and if i wanted something purely for the story and no good gameplay, id just read a book... which is what i did in fact