Disclaimer: reviewing a pre-publication digital proof via Netgalley, so not all images were available, some formatting and text may have changed,etc.
Reading like a classic children's novel, The Wonderling takes you on an illustrated, Dickensian journey of adventure, discovery, and identity.
The character who eventually becomes known as Arthur is a nameless groundling (a talking, humanoid fox child) in a nightmarish prison of an orphan's home. He's essentially good and proceeds through his adventures by being so pure, goodhearted, kind etc. etc. etc. that he wins out over the fiendishly unpleasant and evil cartoonish villains. So, like I said, classic kids lit. Think anything by Frances Hodgson Burnett, but with animal hybrids. Arthur is a bumbling but well-intentioned naif who goes about making friends and allies and more or less sailing through some admittedly hairy situations without much real danger or tension. Creepy settings, but not terrifying. Shoutout to his best friend, a tiny flightless bird-creature - she's an engineer-inventor and consistently saves the day and moves the story along.
The art is pretty, delicate, pencil-shaded drawings (though, as noted, not all of it was present in the proof copy). The story is slow, meandering and dreamy in a probably-intentional way. It's long (again, kids lit of the past-style), with masses of description, and will get varying mileage depending on the reader. If you adore illustrated classics, fantastical worldbuilding and simple, traditional stories, or your kid prefers dreamy fantasies of the past over fast-paced modern thrills, it'll be right up your alley. If you're an impatient reader, or giving it to a kid who's a reluctant reader or has trouble focusing, I doubt it'll hold your attention. Some good ideas around art, music, and hope expressed in a very simple style that either lacks in sophistication and depth, or is child-appropriate, depending on your perspective/age. I didn't adore it, but ten-year-old me probably would have happily spent the time to push through.