Music is irritating, you can find much longer and better loops on Newgrounds Audio Portal, on Freemusicarchive.org, Incompetech.com or Freepd.com; In addition, there are no sound effects - a sound effect for jumping and dying could probably improve the game.
The playing field is WAY too big, on screens with smaller resolution it's impossible to see at once - remember that standards for web developers (who you technically are if you're making web games) is 1024x768! So overall, that made it completely unplayable for me.
Controls are responsive, but they just feel bad. Your character feels floaty because he falls a bit too fast, and he moves left and right to fast to feel like you're completely in his control. Also it appears there is no 'coyote time' and your character falls the instant you walk off a ledge - in platformers that feel well, generally there is 1-4 frames after walking off a ledge where you can still jump.
The core concept is solid - it's the execution that falters.