Well I think any Call of Duty game these days takes the cake. MW3 for me (haven't played blops2 yet). Kept playing because it's easy to pick up and play.
I occasionally play the COD games. The last good COD for multiplayer was World at War......multiplayer has been god awful since then. I play BF3 now. All this is on a PC...I hate shooters on an idiot box.
I have so little time to play video games lately that I don't play games that I don't enjoy. I recall a computer game that my brother and I wasted a bunch of time that was absolutely terrible called Fox Sports Soccer. It only had made up players and the physics behind the game was terrible. More often than not it was more likely to score a goal with a ball that dribbled past the keeper than a well struck ball in the top corner. I don't know why we wasted so many hours playing that game.
Got Angry Birds Star Wars on my droid phone. The worst games I played repeatedly are Who Wants to Beat up a Millionaire on Dreamcast, MLB on NES (from fucking LJN), and Back to the Future 2 and 3 on NES (again from fucking LJN),