Pretty tough but I had fun!
I think it's short enough that being tough isn't too bad, maybe start the first level off a bit slower though. I found I had to die a couple of times just getting a hang of the controls, maybe have the first couple waves not fire back and move slowly so people have time to get a hang of things. (also it's not clear that the debris is not harmful, so I spent a while trying to dodge it xD)