Thank you for taking the time to play our game.
Our plan at the beginning was actually to have levels where you're doing challenges or maybe trying to escape from the lab. But, we had a few time management problems :D
So we didn't really have time to implement any interesting levels and had to go with the current score based wave system. We agree of course that having levels would've made the game more fun.
Thanks again for the great feedback, we really appreciate it. Good luck!