We watched three episodes of the Hilda animated series last night. So, far it's adaptations of the books. Episodes later in the seasons appear to be new stories.
We enjoyed it, but there a few flaws. The animation is not as fluid as it should be. It's not bad, but it's not as liquidy smooth as it should be. Maybe this is from an adherence to the comic's brushy style?
The pacing seems off as well. In Hilda and the Troll especially, I imagined a lot of space between most panels. I imagined Hilda and Twig would encounter a new phenomenon, then stare for a bit. Or Hilda would make an observation, and it would sit for a while. They jumped very quickly from beat to beat in the first few episode.
I think all this could change, though! Adventure Time was mostly just OK for the whole first season.