Well as you know or all know, the Xbox 360 aren't that cheap, so the best is if you have a good Pc buy all games, that comes identely out like the console games on PC version.
At the moment I must say, that Xbox 360 doesn't bring many good games out which are worth to buy my oppinion. But there is one must have who owns a Xbox 360 and that's Gears of War, the Storyline is nothing new there are many out sourcing from Final Fantasy Spirit Within, Matrix Revolution and Chronicles of Riddick Saga. But the gameplay is very fun, because if you aren't that good on tactical shooter like Rainbow Six or Ghost Recon Advanced Warriors, this game is for you, I mean in the eyes, of real tactical pro gamer this game is for tactical noobs, but it's fun, and sometimes hard to play.
I'm not that good in Multyplayer, actually a noob against the others but it's great gameplay. The community is sometimes very rude with beginners, but that is already known in all MMO games. There are some people, who think that the trash they talking prove their strength, but it's POOP. Anyway, the game is the first game with the Unreal 3 Engine, all scencuts are in realtime grafic, sometimes, the Xbox 360 need many time to load the textures, because this game attacks almost on the Xbox 360 recources, well that my point, or maybe it's because I got the Pal version. The Soundtrack is very good, I hope that they will release the Soundtrack soon.
Then I think it's also this year that the RPG Shooter Mass Effect will coming out, this is a great game really I can't tell you which engine it is, I think it's their own engine. It's a mix like Rainbow Six Vegas and Gears of War hide and fire.
Then the new Spider-Man 3 game who comes out soon, but I hope this time the game will release exectely for the PC version , not like that crap from the Spider-Man 2 PC game, honestly this game was a totally joke.
Dead or Alive 4 isn't that bad, but I hate the game, because my favorite character are much weaker then in DOA 3 it's a completely Chinese and Ninjitsu Art mod, so like Bayman and Leon completely sucks in the hole game....
Crackdown has a good basic idea I think but it still a GTA like crap, do this, go there bla bla bla, but if you like this type of game, that game isn't so bad, but I could read on any other thread that this game is very short...
On Xbox Arcade you find also some great games, like Ultimate Mortal Kombat 3, Street Fighter 2 Hyper Edition etc.
Then this year normally if everythings going like it's planed, there comes the last and I think he has some potential to top the first Halo game, Halo 3, and Halo Wars, well actually I still hope that this game comes also on PC out, I prefer to play the RTS games on PC.
Well I think that is it actually...