I had a blast playing this! I love the tight constraints of managing health, xp, and consumables. exploring the world to find the points I can push forwards through is so rewarding. I just finished playing through the challenge mode, making great use of the zero-death reward from a normal playthrough :)
playing this reminded me a bit of Desktop Dungeons in terms of how open information is, and the tactic of clearing a screen of enemies by taking as much damage as you can handle, leveling up from the near-death enemies, and then taking care of the rest. it feels good to pull that off!
I have mixed feelings about the spellbook. I love the tactical variety in it and how powerful it can be, because it can open up so many solutions to getting through tough situations, but at the same time it can trivialize the difficulty... however, I think I'd prefer it being overpowered, than underpowered and thus likely frustrating to manage.
one more thing on my mind... when I was first playing the game, I really thought that all the yellow stones throughout the world would turn out to be important, their placements seemed so particular and obscure. I know they (minor spoiler) visually change when the world changes, but that's all... it was fun to speculate on what they could mean, though!