After reading some of the reviews, and seeing the negative feedback, I don't see how this is a horrid film. Is it as good as the first two? No, but that doesn't mean it's bad.
Music is pretty good, not as catchy or good as the first two (zombies 2 had the best music, then zombies, then zombies 3), but still decent. Dance numbers were fine (note, I don't really care about dance numbers, so I'm really not counting it in my rating)
I get where the people are coming from - yes, this kind of does feel like zombies 2 but just replacing the werewolves with aliens. It's got some differences to it, but they are minor so they don't help that much. Overall, I wish they had tried to come up with a different story, but what they landed on was..fine.
(SPOILERS)
My main problem was addison. Why? Simply, she says "I'll never fit in with my white hair". She had a perfect life basically - loving boyfriend, true friends, captain of the cheer squad, loving family - what more does she need? She already fits in.
I get she wants to find out who she is (her species), but in reality, MANY people would wish to be addison (I mean I think? this is my opinion, please remember that). She really has NOTHING to complain about.
Overall, I'd give it a 7.6/10. Not as good as the first two, and has some flaws, but all in all, if you are a fan of the original two movies, I'd recommend it to you.