This book was a really disappointing ending to a series that had started rather well. I hope that the two prequels will answer all the questions and mysteries that were never solved in this book because I was as interested in the backstory as I was in the Gladers' story. Only the latter is solved and even then their past is left out. The plot isn't bad, but it is in general very predictable and there's only one part that can be consiered a plot twist.
Also, the characters were very different compared to the first book. I can see why Thomas, Minho and Newt wouldn't trust WICKED to return their memories without changing anything, but all that knowledge would have been very useful for them. They never even try to truly find out what the others know. Considering how much time they had spent trying to undestand the maze, it seems a bit strange that they're suddenly not interested in inside knowledge.
Not all was bad though. I actually liked how the book (and the series) ended. It was really good, as it is closed and open at the same time. If you liked the other two books, I would recommend you to read this one too. Just don't expect too much until the last few chapters.