Nice, the slomo feels good and works well. I think it might be better on a specific key with a gauge, so you have to manage using it too much.
I also think it'd be good if everything was zoomed out a little, so there's more going on at once.
I've done stars like this before. If you keep them as a list of random points, when you draw them you can pick a random brightness to draw with, which makes them flicker.
Overall good job, it's fun!