I would give this game a try if you want to play together with other fans of Adventure Time. It seems to be made for multiplayer. I've only played alone.
Okay, so the characters are fun because they chatter as you play them. B-MO constantly making comments on the Wii U gamepad is great. The real voices of the show are here. Otherwise, nothing else made me want to keep playing.
I love dungeon crawlers and watch Adventure Time, but the core of this game is empty and repetitive. The dungeons are dull to look at and explore. Since each floor is basically a big square with changing walls and pits, the boundaries become predictable and there's not much to exploring. The main goal is finding treasure to level up your character.
The other thing you'll be doing is fighting enemies for treasure drops, which they don't do often, so later on you might start ignoring them when you can. If you decide to fight, you'll be facing few different enemies that do the same patterns every time. There's no experience gained for fighting unless they drop treasure, but you'll mostly find it lying around the dungeon floor.
The themes of the levels will change as you continue to lower floors (to ice or caves with electric walls), and you'll face a boss maybe every tenth floor. I had a small itch to continue to see what else was ahead, but after losing my speed token (increases speed) from dying to a boss, I didn't want to continue on at a slower pace.
So, if it wasn't for the talking characters and a bit of the show's humor, the single player game would be a 2/10. If picking up treasure wasn't necessary, I would be running for each floor's exit since I didn't find the fighting or exploring much fun.
But again, I played alone. Maybe gather some friends and give it a go.