Good all round effort! The game was well paced and I liked how you introduced harder enemies.
I ended up just falling to the bottom and running left and right as I fired at 30-45° which made it easy as the enemies just kept running into the arrows.
Also, it'd be nice if when slowing down time the shot strength didn't slow down too, instead it took the same time to power up as in normal time. I haven't looked at your code yet but with the Time class I think there are a few options to use "inRealTime" or something that will still work regardless of how much your Time Scale varies from 1.
Great work!