VERY Original, great job. One thing though. I know this would be almost impossible, but I would rather have a larger story with more campaigns then big campaigns. I'd rather have like 7-8 waves each level, because once you fill up your spots, it's just a shooter with 4 guns.
Unfortunately, I don't really like it. I can tell you put in some good time and the concept is great, but it just seems boring. Since I can tell you really worked on this, I'll give you 3/5