It's an immensely fun game, but there are some definite things that could be improved upon. Firstly, I think the reason people are complaining saying that the jump only works half the time is because there's no leeway letting you jump past the edge, which in a game like this is pretty important. Secondly, the collision with those mouth enemies is so annoying, I was eaten so many times when I was pretty sure I shouldn't have been.
But the worst thing, by far, was the random avalanche system. On what I think was the last level (I'm not sure, my browser crashed and I didn't realise it didn't autosave), the amount of times I ended up getting screwed over because it decided to randomly drop giant boulders on the platform I was standing on or jumping to was insane. The one time I almost made it to the end was because an avalanche decided to only drop 3 small rocks that I easily avoided. On a game that's so based upon memorising a routine to make it through the levels, the randomness of that really kills the flow of it.
But aside from those, it was a very fun game, challenging and a little frustrating, but not too frustrating to make me rage quit. Almost. That avalanche stuff really is a bitch.