I was gonna rate a five, until I got to wave 20. Those kill bot things are WAY over powered, when the rest of the units are underpowered. They deal 50 per hit, shoot rapidly, have tons of health, and have a deadly spin attack that is almost impossible to avoid when there are several of them doing it.
I accidentally pressed spacebar during the cutseen after beating the fish boss, so ive missed about 1/5 of the story. Why would you make the skip button spacebar?!