First of all, congratulations on making this game. It's quite ambitious to create so many levels, enemies items, and even a boss in just 48 hs, that was really impressive!
I liked that you created a risk vs reward situation with the chests, in which you can either rush through levels, but if you do so, you don't get any upgrades. To further endorse this aspect, I would suggest you to, instead of having you having your hp reset every level, give the player more hp, but it doesn't heal every time, thus making the player having to manage more carefully its health.
My big problem with the game tho was the gimmicky way that you take a key away at random. I understand that you tried to give the player an interesting choice of pressing space to spare a key, however in most cases this decision is pointless, since if you lose a movement key you're screwed. That`s even more evident in the boss, where you take a long time to defeat, and most certainly will lose an important key even before taking half of his health.
But overall, that was pretty fun game. Cheers!