Third, following Obsidian, for Finn & Jake.
Well, Finn. Who's old, nearly dead in some dungeon, and goes through to Hell looking for his long-dead brother. Instead he finds a bunch of returning characters who are all dead, including Tiffany (sigh) as the main rival/annoyance.
The designs of the Hells, "Dead Worlds", are fantastic, except the crappy 1st one, but you don't get to spend long in each, there's no exploration or sense of wonder, just fancy backdrops for a few death angels & New Death chasing Finn who's chasing Jake. The cosmology is sort of Buddhist by way of Dante's Inferno; but it's never explained enough for that to be a major element, either. In the silly 12-minute episodes, they could do a long dreamlike song or mystical exploration, and then next ep be back to kicking butt. In these 46-minute movies, they don't really seem to do that.
It is nice having the brothers back together, having adventures.
But, BMO had a great setting, kind of a good story, but terrible characters other than BMO and the bugs. Obsidian had a boring setting, boring characters except P.B. and Marceline, no plot. This one has the best characters, a plot… but an unexamined setting. Are they doomed to just make sequels with different failures?