This is good. Like really good. Missing a bit of the charm that makes Adventure Time so great, and everything that makes JJ Villard my favorite artist.
I theorize that they make this stuff for fun on the side, because it's pretty much how they like to spend their off-time. Only they also get paid for it...
They have a huge writing staff, and also season 5 was weird because it was twice as long as a normal season, and remember that their episodes are half the length of a normal show, so really each season only has the equivalent of 13 episodes usually.
Also all of their best writers have left for other projects, and so the main show hasn't been as good for a while. It's still decent but the last few seasons have just been okay, rather than absolutely phenomenal.