Very clean, very fun. I was pleasantly surprised to keep finding new things the higher I went, and I wonder how much I may have missed further up (I got around 6000 score). A little bit of delay on the game over screen might be nice so players don't accidentally click past it and miss their final score.
I think we had some similar design ideas (such as allowing ANY key to be used). Maybe you could give my game a look and see how they compare :)