Hi and welcome to the forums.

Can't see Batman Arkham Asylum or Halo ODST getting many votes mate as there not out yet.

My top 10 Xbox 360 games are (in no particular order) :

Call Of Duty 2 & 4
Gears Of War 1 & 2 (although i'm rubbish at them !)
Virtua Tennis 3
Burnout Revenge (hated paradise)
Guitar Hero Metallica
Rock Band 2
Soul Calibur IV
Streetfighter IV
PGR games (preferred 4 but the bikes were rubbish in it)
Left 4 Dead

Others I have enjoyed are :

Dead Space (fun but limited appeal once you have completed it)
Flatout : Ultimate Carnage
Army Of Two
Devil May Cry 4
Mortal Kombat Vs DC Universe
Pure
Forza Motorsport 2
Lego Star Wars,Indy & Batman
Colin Mcrae : DIRT
Ghostbusters
Moto GP 08 (but 06/07 were unplayable)