Fun, yet glitchy.
I would say that it is a well done engine overall. But here are the glitches that I found.
1) Running straight to the steps that lead up and into the next room sometimes has the character running and falling off the ground, only to fall back into the stage from the top.
2) Leveling up increases your health, but the enemies still do the same percentage of damage which negates the leveling up 's purpose.
3) I leveled up a lot, as in I clicked the button a lot. That seemed to send the character into an endless loop of level up animations. It seems that after the fifth click or so, the character doesn't stop doing the level up animation. The only way I could bring him out is by exploiting the next glitch.
4) Pressing pause and then unpausing seems to make the character disappear and reappear in the same spot. I don't know what causes that, but it seems to be a way to get out of glitch 3.
5) After leveling up many times, my health still remained at 100. However, at this point whenever an enemy attacked me, I GAINED health instead of losing it. That and the health bar shot past it's set frame and went out of where it was supposed to be. Perhaps adjust it so that it will all fit into the one bar.
The game engine was alright otherwise. Enemy strengths could be debated, as shown by the laser skeleton that was severely overpowered. In any case, with some more improvement, this can become a full fledged and well made game.
-HFX ^_^