The answer lies in the Tone, the Toll, and the Thunder.
These characters have really grown on me. I love Citra, Rowen, and Greyson so much. These three honestly make this series. Without these amazing characters; I really don't know how good these books would have been. And I just have to say, thank goodness there was not a lot of scenes with Goddard - I hate his character so much and Shusterman did a fantastic job creating the villain. The characters definitely had changed a lot from the first book but in such a way that I really felt like I grew with these characters. I'm so glad that I picked up these books and read their stories.
Overall, The Toll by Neal Shusterman was a fantastic close to this trilogy. While I was expecting something a little more epic like the last two books, I was given closure and that I can be happy with. It wasn't an ending I was expecting but our heroes should be happy and I hope they are. After going through all these events with Citra, Rowen, and Greyson, I've truly come to care for them. I highly recommend this whole series if you are interested. This was such a great adventure, as frustrating as it was sometimes - but the best stories always are.