What video game should I get?

Ok, so I have a PS3, and I realized that most of the games I have just aren't that great. (Save Fallout 3 and Metal Gear Solid) I used to be an Modern Warfare 2 addict, but I lost the disc and all I have is World at War for a decent FPS. I'm looking for any genre of game for the PlayStation 3 or a Macintosh. (I was considering The Orange box, since it's on steam now) I want a game that will keep me hooked for months. Help! Please, I need more detail. I''m so indecisive