It was two titles at the same time actually (bought them with my PS3)
Metal Gear Solid 4: Guns of the Patriots (simply because im a huge Metal Gear buff and I wanted to know what happened next after I left off with Solid Snake and Raiden in MGS2... However in retrospect I didn't find the game to be quite as good as Metal Gear Solid and Metal Gear Solid 2: Sons of Liberty. The cut-scenes were ridiculously long at times and didn't really contribute much to the story, also some of the supporting characters in the game were a bit too much for my suspension of disbelief to swallow, then there's the fact that while you can collect a ridiculous amount of weapons the sheer variety doesn't exactly fill any purpose in the game. Still the game was far from utter shite, but I feel that it could have been a lot better)
AND
Army of Two (which probably wasn't the most "game for buck" gaming related purchase I've made, but the game is very fun to play in co-op mode which was the primary reason for getting it, so...)