I do game dev. as a hobby and thought your game was cool! Here are some of my thoughts while playing:
Your jump height felt fitting to the game, but perhaps lowering the gravity a touch would make it feel better. Also, it is usually better to make it so the longer you press jump the higher the player jumps.
The magic was cool- it reminded me of the original Kirby series on NES! I think that you should have a cool down or a limit on how many times you can use it. Maybye have the small enemies drop magic refills of some sorts.
I thought the item collection was cool as a goal for completing the level- If they were called something other than items I apologize I skipped the story XD. Maybe have each level devided into segments, and each segment has a mini boss in it. in order to obain the items you must kill the mini bosses in each segment of the level, then return to the beggining of the level and use your key to open a door. the door opens up to either the next level, or a boss monster.
Just some food for thought! I hope you find this helpfull, and keep me posted on how this game is coming! Pls post all new versions you make!