There are so many differing reviews here, covering everything from awful to excellent, it's going to be difficult writing anything new. So, I'll not try and just say what I thought:
I quite liked the idea of a group of kids making zombie movies and the comradeship that brings and we see them getting along for a common purpose. Some of the scenes between young Joel Courtney's and Elle Fanning's are touching, believable and very well acted, whilst the others offered a ragbag of youngsters that are typical of a traditional Spielberg.
The military/scifi elements might not be totally new and unique, but to my middle-aged mind were put together well enough to seem fresh. The SFX were good enough for what was needed, though not exactly state of the art.
Enough went on and mostly suspenseful enough to keep me interested and ultimately, I enjoyed it for what it was. My rented DVD won't be replaced with a copy of my own, though and I give 7/10.