It's not even close to the end of the year yet, there's still a bunch of games that could take that title that haven't been released. Such as, MWF2, L4D2, etc.
thara is this new game (it's not out yet) but it looks good, its called rage follow this link http://www.gamespot.com/xbox360/action/idtech5/news.html?sid=6195316&mode=previews
that game is fun. literally everything but the landscape is destructible!! the fights in guerrila are sweet. and it is fun to bunker down into a building at red alert with the stairs destroyed so they can get to you. meanwhile they are shooting at you like mad destroying the building. eventually the building will collapse with you in it (maybe) and you try desperately to charge head on into the swarms of EDF troopers trying to snag an empty car than drive off into the sunset while EDF guass turrents and tanks are blowing you to smithereens.
Do you mean flash game? I don't know yet, I think it's too early, but I am a big fan of the Submachine series (pastel games fan) and Mur said he'll have "Submachine 6" released in 2009, so I'll have to go with "Submachine 6"!!
Otherwise, I also liked "Morningstar" (yes, I like PnC games best!), and "Knightfall 2" was quite addicting too... I can't remember any other right know..
modern wafare 2 is goning to be the game of the year because its got all this hype from the ppl who liked COD:WaW and those ppl who didn't like COD:WaW and think COD4 was still better.