My feedback is pretty much the same as pdil. I enjoyed the art style and the extra dimension. The combat felt pretty good, with nice animations and a variety of weapons that all felt distinct. I bet it would feel really nice with some SFX.
I got stuck for some time on the "crystal jump", and even now I'm not really sure how it's supposed to work. It seems you have to stay stationary when you jump, get the timing for the attack just right and then input a direction? It's very hard to pull of, which is a shame because I figure it could be used during combat to avoid enemies and attacks.
But just like pdil I gave up in the room with the weird blue-ish shape. I was expecting to collect an upgrade that would let me use the metroid-shaped thingies, but I just couldn't figure it out, despite pressing all the buttons on my controller. All the other abilities had a tutorial popup explaining how they worked, but sadly not this one.
Still, a nice-looking entry that would make for a pretty interesting game with more polish. Keep at it! :)