Great start! I'm liking the effort you put into the lighting. Here's my notes.
- How many enemies is appropriate per level?
I don't think I can answer this quantitatively--whatever is a good balance of "rewarding to beat but not frustrating"! I think really nailing down how you expect players to use the provided mechanics to win will naturally lead you to the right answer. - Would you prefer a HUD?
Once again, I would rely on the mechanics to determine this. If you find that your solution is to provide more and more HUD, maybe consider simplifying your mechanic. - How strong should the enemy attack the player?
Currently, I think that the strength of the enemy doesn't matter, I simply bypassed the enemy. Maybe focus on the clarity of how the player should engage the enemy? I assumed that I had no ability to combat the enemy. - How should the player attack? Would you like mouse click combat or full keyboard combat?
I would prefer you to make that decision for me :). Whichever one you think will make a more rewarding combat experience. - How do you feel about the jump height/power? Should it be lowered?
Jump height is fine, as long as I can make it up the stairs somehow. I got stuck a lot and ended up flinging myself off the side of the stairs into the lava so that I could get back to the start.