Extremely good game! I had a lot of fun playing the game. The progression works extremely well and each item gives you its own really useful ability.
The only small criticism then is that the boss fight does feel way too easy. After slogging through the dungeon for a long time and mastering the abilities, I didn't lose a single heart due to the shield in the final fight. Given the theme of "boss", it could have taken a more central role and been a bit harder. But that's complaining on a high level.
Otherwise, the game looks top notch, and above all, feels very good to play. I especially like the bouncing off the walls.
Great entry, it was really fun!