Not bad....but
It needs a lot of work, but it's a nice start.
Try to add a game over screen, at the moment, when the character dies, it just remains on screen.
Audio optimisation would be nice as this submission has a very large file size, for something relatively simple. It ought to be compressed, or perhaps use a loop from the audio portal to lower the file size and make the loading times much quicker.
Also the block can go off the stage, on the right hand side. Which makes it quite easy to avoid the circles. So a small improvement to stop the block's movement when it reaches the stage's boundaries would be an improvement.
And lastly, the graphics could be redesigned, perhaps add colour.
But I like your code, it works, and the variety of the enemies size is a nice feature, as is the fact some fall faster than others.
So this is a nice start, but there are just a few pointers that could be improved to make a much better game next time.