I like what you've got so far! Some text about which keys do what would have been helpful, I did find that 'Q' activated slow. on level transitions if you have more than 5000 slow it sets it back to 5000. And if you activate slow just before a new wave loads you will start that new wave with infinite slow, and it may have also crashed it. I might also suggest making the enemy shots look a bit bigger or remove the green stars from the background, there were a few times it was hard to tell if a green dot was dangerous or not. Sounds are spot on though!