I like it
It would be more interesting if the enemies would change faces, also include more easy-to-achieve upgrades for your character like a red bandana or a sword or something. a really good makeup would be slow-motion-battles against bosses and levels. since environment is changing all the time why not include levels like running for 5 minutes or so... and then a boss! This would spice it up!
Anyway I like your game, very good idea!