This game is really good. It's intuitive, easy to learn, and chock-full of the clever design that separates good metroidvania games from bad ones. I love the way two rooms are reused, but feel totally different after you get the powerup needed to take their second exits. The boss (I named her Rosa) is a lot of fun, and quite difficult. I've never seen a boss that requires you to wall jump, and the first phase was a lot of fun to learn and beat.
The second phase was also a lot of fun, but since you get the airjump powerup in the boss room, you don't really have a chance to learn how to use it, which makes the second phase kind of frustrating. I'm also pretty sure the health bar extends past the screen, so you can't tell if you did damage the first few hits (apart from the subtle red flash that's easy to miss if you're not looking for it.). I've only beaten the second phase once, but I've beaten the rest of the game at least six times.
The second to last room before the boss, with three enemies in it, doesn't seem to work as intended. You can hit them through walls, and the last enemy is inconsistent in its behavior, which makes it hard to beat/walk past without taking damage.
The last issue I found was that the game runs at different speeds on different computers. On my laptop, jumping is slow and bouncy, while it's so fast on my desktop that I'm pretty sure that the game eats my inputs sometimes.
(This might help with that issue)
I also had to rate one star for sound because there wasn't any.
I know I just dropped a lot of criticism on you, but the game is really good, and the issues I've mentioned shouldn't take too long to fix. It's surprisingly complete and polished for the time and file size restrictions, and the level design is some of the best I've seen. Period.