I played through the entire demo.
My favorite part of it was the final boss fighting "Dr. Moneybags". I was wearing the gun hat and it shot at him, interrupting him mid-conversation. I liked that there was an actual reaction to it in dialogue. Also on a related note, I wasn't able to see the full cutscene when he was defeated (because the gun hat destroyed him before the cutscene was over). It was funny, and hopefully that doesn't cause sequence break issues.
In terms of bugs, one thing I found was after beating that boss with spring legs and entering the room with the lore machines, somehow exiting that room caused me to get stuck underneath the boss door which had respawned. In fact, the sequence relating to that particular boss fight felt quite buggy in general, at least from my experience.
While combat was enjoyable enough, all the abilities you get whether that be the Eyes of the Shapeshifter, Hats with different effects, or that ladder arrow are really the things that kept me playing.
Hope to see more of this.