Great game. I suggest just playing any of the two first depending on which one someone prefers. I started with hard because I thought that the other one was only if you were gonna vote on lundumdare
I enjoyed it on hard and I think relying on skill is a lot more fun (and heck, if you find it too hard just lower the difficulty). It was short but nice.
I suggest not trying to make the game too hard for you guys. Sure you can beat it in one life and you'll get a better reward, problem is that you are gonna be slow because by playing on hard you are gonna be trying to be careful. It's more fun to give yourself at least 3 lives and then just when you learn you actually start acting fast. I think I would had enjoyed it more if I didn't always chose that difficulty
My only suggestion if this was meant to be a fully fleshed long game is to have more skills and a bit of story (not story, just a bit of maybe background). But for a short game this is right on point, short metroidvania games don't need these things (specially since you really wouldn't be using them for long...). I really like metroidvania stuff (also, last boss is not hard or tedious, you just gotta git gud and try new things to make more damage)