Ok so what you have is a good idea, but there are some isues. The hitboxes of the terrain aren't correct every time (get stuck under ground, glitch through blocks), It's also a bit annoying that you have to start over when you die, I'd reccomend having (some of) the files set a checkpoint. Last, the game loaded slow in browser but I'm uncertain whether that can really be blamed on game design.
It really is a good game, especially when you think about the time you had to make it. It's fun to play, but it does need some work.