This is a neat game! It's an easy recommendation for any fans of the Metroidvania genre and it can be 100%'d in about 10 hours. The style is really the main draw here, it feels like something pulled straight out of Grimm's Fairy Tales, a feeling augmented by the fact that one of the things you're collecting are literal pages out of these slightly sinister children's books. These pages tie nicely into some of the characters and areas you run into throughout the story as well which is a nice touch. I enjoy that games like Elden Ring have pages and pages of lore sprinkled throughout item descriptions for people to seek out if they are so inclined, but it's also nice for a game to just put together a simple story that I can clearly connect to what is happening around me. All of the bosses and enemies fit perfectly into this theme as well. They're all extremely weird, fucked up guys with stuff grafted to them or way more teeth than they should have and it rules. The very first boss is The Gardener who's a guy who has been turned into some kind of gardening spider with scissor blades for limbs. There's a wide variety of areas that explore different aspects of this style as well, from sewers to an abandoned castle to a dollmaker's house.
For better or worse (I lean better in the case of this game but others may disagree) the game is rather frictionless in that it moves you at a quick pace. I played on Hard mode and most normal enemies were able to be defeated after dodging at most one of their attacks or by using your Vessel (essentially special attack in the form of a Molotov cocktail) to one shot them. The platforming sections were all pretty light as well, especially if you've played Silksong or games of that nature, which can be nice! It keeps you feeling like you're constantly making progress and discovering new things. But I do wish they'd gone a little further with the challenge of those sections, there's no extended platforming challenge section like in MIO or Hollow Knight for you to really put your skills with the tools they've given you to the test.
I do have a few other minor quibbles that I think hold it back from being something really special. First, the boss fights all feel fairly similar. They all pretty much have the same few types of attacks: one that makes you dodge falling items, one that you have to slide through, and one that makes a shockwave you have to jump over. This leads to them being very little challenge even on hard mode after you get the hang of it in the first one or two fights. As previously mentioned, all of the boss designs are incredible though so that monotony is mitigated nicely by beating up on some real good freaks.
Second, and probably more importantly, other than the overall style I just feel like this game doesn't have anything that truly sets it apart in a very crowded genre. The style is great! Don't get me wrong, I love the macabre vibe that it has. And I don't think every game necessarily needs to reinvent its genre, but I do think it's hard to say a game really reaches special heights if it doesn't bring something unique to the table. But it is a very lovingly crafted one of these and there's nothing wrong with a game just doing a well established thing well.
Overall, if you're craving a Metroidvania that you can get through in a very reasonable amount of time, you'll have plenty of fun with Well Dweller. I haven't played a Kyle Thompson game before but he got enough of the core Metroidvania things right with this one that I would be very excited to see him try his hand at the genre again and discover where he would take it.