That's a nice take on the theme. The upgrades feel genuinelly impactful, so I like how there is some strategy to taking damage. Excellent visuals and animations - very juicy - especially the background graphic and the menu and death animations. Simply - excellent work there ^^.
One thing that could use some more work is the level design - it's very confusing, I kind of got the idea that I should be heading down and to the right, but I was feeling very lost. A small thing that would help a ton, would be to have some parallax movement of the background - it feels very weird when you're jumping, moving all around and the background is completely static. That definitely adds to the confusion. Another thing that I found and I'm not sure it was intentional -if you're next to a wall and mash [up] you can climb walls. It kind of looks like a big, but if you give it it's own animation you could call it climbing :p