Biggest change between books one and two, single to dual POV, and it was perfect. Reboot was told completely from Wren's POV, but in Rebel we get both her and Callum. I had mixed feelings about this. I didn't care for it at all in Allegiant because of what I felt it did for Four's character. That's not the case here. It actually made Callum a much stronger character in this case. We get to see him grow into a real leader and someone who can make tough decisions instead of just being the guy who reminded Wren of her humanity. It's also fun to see Wren from his POV because it shows how close they've grown and how well they know each other.
If you read the first book you know there's going to be action and romance, and Rebel continued that perfectly. The romance is sweet but it never overtakes the plot. It simply helps move things on a bit, not that the action really needs any help. It's tense right from the beginning, with multiple villains and shades of gray. If it isn't one problem, it's something else. I've said it before, but I love when no group is perfect. I won't give too much away, but I really like the way the different groups Wren and Callum are portrayed. A lot of them have great people, but there are always the corrupt or fanatical that keep our main characters on their toes and no place is safe.
What's best about Amy Tintera's series is (maybe) that there are only two books. Part of me really wanted more, and I'm excited to see what she does next, but there's a part of me that is relieved. A lot of dystopia books have sort of meh endings (I'm looking at you Mockingjay and Allegiant). This one goes out with a bang, and while I love how it ends, full of realistic hope and change, I'm sort of glad there was no bad middle book or frustrating ending to taint the series for me.
So should you read this series? Absolutely. It's a fun, unique dystopia/zombie (sort of) idea, where everything begins horribly but ends with a sort of hope, which is just the way I like my dystopias. I'm giving it a very strong 4 stars and would recommend it to anyone who wants an action-packed read with just the right amount of romance thrown in.