Not sure why the slimes turned into black holes, but it's a creative idea! Seems to have an appropriate difficulty curve.
The gameplay works, though the gun tends to have an offset to where I'm clicking at. It was pretty funny how the game just broke when a black hole got big enough!
Lack of music is very noticeable, as is the lack of ambience and other sound effects than shooting.
The menu background color changing according to the difficulty setting was a nice touch.