Halo 2 is by far one of the better games out on the market. However, it does wind up a bit short when tallyed up with what it is and should have been.
First thing, the game feels and plays basically like the first, FPS using both analog sticks and left hand for grenades and right for weapon. However, the left hand is now not only one for grenades but you can dual wield. Dual wielding is big because it factors into how effective you can be when you attack someone. Also another new feature is the ability to lock on with rockets, which make targeting a little easier. The game is xbox live compatible which is the meat. The game's campaign mode, being only 10 hours long, needed to have good multiplayer and it came through. ONLINE you can have varieties of Modes to play in such as Rumble pit Every man for himself, Team SKirmish 4v4, Big Team Battle 8 v. 8 and dozens of more.
Halo 2 of course has some new maps such as the foundation one in which you get when you first enter XBox live. Also a few new weapons such as the Energy sword which is a one hit kill if used with the lunge technique.
Anyways, halo 2 is definitely worth 50 bucks. Just don't get your hopes up, its no innovator