Awesome game. Just rented it from Gamefly last week. I just wish it was longer. I finished the game in 3Hr 39min, collecting all upgrades and completed 100% of the game. I did not complete new game+ mode though. If this had been a 10-15hr game, it would have been epic.
Because of the short length, I recommend most people wait until the $10-$15 range.
P.S. - Prior to this game I knew nothing about Adventure Time. Even with that said, the dialog and story was hilarious and well done.