Halo: ODST is an expansion for Halo 3, so if you don't have Halo 3 to begin with, the expansion will be pretty much pointless for you, if you really want to buy a game right now just for fun while you wait for MW2, you should try buying a used copy of Halo 3, so that way it's really cheap. I think brand new copies cost around $40 so a used one should be around $20, not bad just to play for a few months. But if you want good practice for MW2 you should buy COD4 (used copy) to get some practice for MW2 because the gameplay will be close to the same with some improvements in MW2 and World at War's gameplay is completely different from the two, so you might get frustrated at first.