Call of Duty 4. Why the hell would you go for Halo 2? Just compare the reviews! That's reason enough.
Samus, If you're going to be playing this game as well, you better pay for half of it. Why should your brother/sister let you play if you don't give your fair share? If your sibling pays, it is their property. Honestly, If my sibling didn't pay half the price for the game, I wouldn't let him play at all.
EDIT-Hypershock, I seen your usertitle and seen that it said "future marine". Wanted to let you know that when I get older, I hope to persue a life in the military as well ^_^.