sell halo 3 and get COD4, and then if you have spare change, save up for the new Battlefield (bad company).  it features a fully destructable enviroment, yes that means if someone is hiding in a house and you have a tank, feel free to blow the house up until the dudes just sitting in the bath tub
but seriously, get duty, i personally have 5 days into it (1 day = 24 hrs), others have well over a month of thier lives buried in this game, why? because its the bomb digity.