Great arcade-style gaming
This is a really good game. I enjoyed it a lot and I think you've got the difficulty level just right. Well done :)
1. The overall pace could be slightly faster - especially at higher levels.
2. I've played this three times and on one occasion the game simply stopped creating more circles at the end of level 6 - I sat around dodging stars for a while then gave up. I thought this was a bug but then noticed a similar thing at the end of level 23 that turned out to be due to a white enemy off-screen that just didn't come back for a very long time - so perhaps you should restrain their out-of-sight travel a bit more.