Besides the awesome animation style, out-of-the-box story telling and just about the best kid-friendly one-liners ever, the show is also extremely avant-garde, conceptual and imaginative. Take for example Jake the Dog and how he seems to to have no limits to shapeshifting at his own connivence. Having worked with kids, this is like a dream come true - to be friends with a talking-dog who can transform into anything he wants during times of crisis.
The show is also clever in that the humour in it is campy without being cheesy at all. Both the characters are already so genuinely sweet and decent that the show never try to insert preachy moral lessons like most of kids shows which gets super trite and stale very quickly.
If you haven't seen the show yet, you owe yourself to do it. I've always been a big fan of cartoons and Adventure Time is so weird and cute that it suits anyone who identify as those things.