IMO, this wasn't as good as the previous two books in this series. About half of it was spent covering about six months worth of travel in the desert...it had a LOT of repetition. Then, in the last quarter of the book, when it was reaching the climax, months of travel were covered in just a few dozen pages.
Add to this that one of the two main characters seemed to go through a personality change, while the other hardly did more than mope it the background, it just wasn't as interesting as the first two. Once it neared the climax, though, things picked up, and moved along relatively swiftly.
For a novel of nearly 800 pages, it could have easily been reduced by 1/4. If it had been, it would have made for a faster paced story, and wouldn't have been bogged down with so much repetitiveness.