Its good, but the thing is, the enemies don't hurt me. I know you haven't yet finished this, but when I got to egg corridor and got hit by white thing I took 0 damage. And now I am a god.
The RPG part is in the First Cave only.
It's hard to program an RPG in Cave Story's engine, even a real-time based one.
I'd have to use only enemies that could attack from afar, though, like the Labyrinth Critters. Or maybe those fans. Or flying Gaudi.
Who knows.