Levels are too long and if you mess up you don't even get a single star.
It would be way better if the levels were about half as long and there was a way to earn stars even if you die, similar to in other games where you can level up even if you aren't really winning.
As it is, I don't want to spend 15 minutes playing a level to see if a certain defense works and then get nothing, so I'm going to play games other than this one.