1. Optimize the game. At a certain point with lots of projectiles on the screen the game becomes almost unplayable.
2. One stupid, ridiculous thing: if you upgrade yourself just a little bit too much you are killing the boss too early to get all stars! Now what? Am I supposed to reset all the progress and start from the scratch? There should be at least enough minions to get them. Generally, stars on the boss levels like these is not a good idea. In case described by me: at least add a button for resetting upgrades without resetting the progress of the game. -- star for this issue.
3. It is possible to move to the border of the screen and not be able to move anymore.
4. Another bug: few times the game displayed both the victory and defeat screens.