Hi Stefan.
Nice work. Very smooth gameplay, all of the powerups are cool. You have done a lot of things right. Very fun using multi-ball.
Using the mouse was ok but personally i prefer to use the arrow keys for a game like this.
There was a little bit of glitchy movement but im sure you'll iron that out in time.
I think you should probably speed up the default ball speed - having the option to slow down/speed up with powerups are great but unless you have multiball they can pop a bit slow on later stages which in turn made the gameplay slow (slow speed also makes it very easy).
Oh and P.S it was VERY 80's! I know the title screen says left click mouse but all i was seeing was "INSERT COIN" :)