I really like the design and mechanics of this game. It also feels very metroidvania, I think you nailed that pretty well.
There are two suggestions that I think would really improve the game:
* More checkpoints! Since this game has lots os precision jumping and platforming, sometimes it can get very frustrating. Having more checkpoints would make the player cherish each small victory, IMO. I do think a lot of people would disagree on me with this one, though, haha.
* More visual feedback! The deaths are so instant that sometimes they didn't give me the time to notice what I was doing wrong.
Other than that, really solid game. Great work!