Very charming. The abilities were straightforward and intuitive, the enemy types were varied, and the graphics while minimal were still pleasant to look at. The sound effect on getting hit was a good piece of feedback and the damage seemed reasonable. I also liked that the health upgrades gave you another entire bar of health, felt very Metroid energy tank-ish.
I had two issues which I see others have mentioned as well, 1) the movement speed was too slow for my tastes and 2) after I died I respawned at the beginning despite having reached what appeared to be checkpoints.
Overall good job, I was enjoying the game up until I died (I was technically still enjoying the game, I just didn't want to replay the content again). :D