This is by far one of the better efforts on the App Store for a FPS. It takes Call Of Duty: Zombies and makes it more affordable. I really enjoyed this and it is clear that a good amount of effort went into it. Looking at this Developers other games, it seems as though they are a quality Dev.
Having said that, there are a few things that must be fixed.
First, you can not aim and shoot at the same time. I see more and more FPS games release on the App Store with this massive flaw and it always boggles me, especially with a game like this that demands precision. In a game like N.O.V.A you can press the fire button and continue to aim while firing. You can not do that here, so you constantly have to decide what is more important, aiming or firing.
Secondly, the fire button is not very responsive. On multiple occasions it would not fire at all. Most of the time it would just stop firing for a few seconds even though my thumb had not moved.
Lastly, the hit detection is off. A zombie would be directly infront of me and my cursor would be directly over him and I would still miss. It seems like a game of chance, even when you know you are dead-on accurate.
As a whole, I really enjoyed this game. The graphics are great and the sound is great. These problems hold it back from it's true potential.