Played this for a bit, here are some issues I noticed:
1. Player hit knockback and climbing ladders should be a bit faster imo, pretty much everything else controls great.
2. No screen size options? (there's only fullscreen)
3. There are no pre-boss checkpoints?
4. Maybe add an "external soundtrack" option?
5. Collision for getting on ladders doesn't seem to work when holding left/right and up/down near one, this was a bit annoying.
6. There should probably be an option to make transition speeds faster.
7. Player weapons are broken on other characters, probably already known but just in case.