Really simple, but it works
I see how this can me really nice practice, but it's nothing special whatsoever. It's a simple sidescroller, with quite generic enemies, it doesn't have many flaws, but it could do a lot better.
Biggest issue for me is how incredibly slow you move. It feels tedious and takes forever to move along the map. The enemies are very generic, there really are only two unless you count the boss, which I found way to hard, mainly due to the very poor controls.
The level up system doesn't seem to do much, it heals me, and sure, it might make me stronger but there's not way for me to find that out without a damage counter of sorts. The game is so short that a proper level system wouldn't do much anyway, and leveling systems aren't normal in continuous 2D scrolles like this, unless it's separated in levels where you can upgrade in between.
The background music gets quite boring, the graphics are really, really simple, and the story is about as thin as it can get, all pretty important for an "RPG" sidescroller like this.