Read/Reread for my own curiosity, comparing the three major Nancy Drew series. (The original yellow hardcovers, this one and Diaries.)
The case was interesting, as it's not very often that Nancy gets to solve a missing person case. I also did like the stuff that you actually learn about the Anasazi, Hopi and Navajo.
However...a lot of character's actions in this book made no sense. Just as an example, Nancy does little to keep her sleuthing a secret. She asks questions, doesn't try to be circumspect, and flat out tells three people (I think it was three, might have only been two can't remember the scene sequence right now) that she is a detective. Then when another character figures it out that she is a detective, she is determined that she needs to lie to him. What worse? He is most assuredly not a suspect.
There's a lot of other odd reactions and Nancy jumping to odd conclusions with little to no suggestion that she's right. She does halfway solve the mystery, which is better than her habit in the newer books of literally just stumbling over it.
Comparing this book to the other two series... I think my favorite might be Diaries - even if Nancy does pretty much stumble over every culprit - because I like the attention to the characters. In this book, Ned, Bess and George are all much like they were in the original series. (Bland, girly and sporty, respectively.) In the newer books, Bess and George especially are allowed to be more, to challenge the status quo of their personalities. And I like that. (And Ned is always bland as bland could be for me, but at least in Diaries he has a family that livens him up a little.)