I really like this game,though, if you do anymore for it, one thing I would suggest is to make boss sections pause generic enemies and have another way to indicate a "checkpoint" instead of the tunnel wall, as the game doesn't stop and you can be hit from enemies while inside.
IMO just having text flash on screen would be fine enough. You could make it that any enemies in the tunnel with you are destroyed, but that could ruin bosses or whatever
Otherwise though, I really like this game and hope it gets more work after the jam!