But I'll admit that's probably a personal failing. But that does point to what I'd consider a flaw: if it's a game that involves continuous shooting, why not just allow full auto? Especially on the FIRST LEVEL -- I mean, I just stopped there because it was so repetitive.
Also, it seems odd to have a timer AND "waves" of aliens. If it's timed, it should end when the time ends. If it's waves, you should just know how many waves you have to survive. "Waves" should also have breaks between them, which would allow the player's finger a REST!
So I rank this squarely in the middle: 5/10. It seems like it has potential, but it's a little too frustrating from a gameplay point of view.