It's a fun enough little game if you liked Gauntlet in the 90s. But this doesn't bring much to the table to recommend it.
If you love Adventure Time, you'll be happy to know that the voicing, writing, and general feel of everything AT-related is spot-on. You'll also be sad to know that it's only tangentally related to ANYTHING, and this is just a pretty average Gauntlet-style dungeon-delve with an Adventure Time lick of paint and far less action.
It's clearly meant to be played co-op, so your mileage might vary, but for the solo adventurer? Give this one a miss. This thing is full of padding. There's little to no variety in the dungeons which are over-large for your movement speed and biomes drawn out too long. It makes use of an RPG-style upgrade system, but with very few increments and they've borrowed that infuriating mechanic from Rogue Legacy where all your currency is reset every time you go to town.
Overall, it's just not very fun.