Well it just feels unfinished. This would be a great 1st game, if it is.
Graphics are a bit too simple, a good rule of thumb is to spend as much time in graphics as in code. The graphics aren't bad, but they are just very simple.
The motion seems okay to me. The hit detection was frustrating though. The enemy balls seemed to hit me from about 5-10 pixels away. Meanwhile, if you jump at the wrong time you fall straight through tiny moving platforms, even if you land right on them. This could be improved by adding an invisible box of the same length but greater width (e.g. stretch it down), or by finding a better way to perform hitTests.
All being said, this is not a bad game, just needs a few more levels, more complex art, and better hit testing.
And if you have time achievements are always fun :)