One warning...this is a book that is recommended for 8th - 12th graders, but it does contain some bad language, violence, and sexual situation. Personally, I would say for upper high school...I think it's a little mature for younger teens.
But, I bought this series for my husband who got interested in the Tomorrow series after seeing the preview for the movie of the first book. It's a great story and very enjoyable for more mature readers. If you enjoys stories similar to "Red Dawn", you might well enjoy this series. It's pretty well written and we've enjoyed them.