This book presents some interesting information, but not having the survey instrument, the actual data, the demographics on the 1200 member study sample or even an index erodes the book's value. There is a lot of "filler", such as more than 10 pages devoted to a description/history of various media. There are a lot of negative references to the Baby Boomers.
If you know the Millennials, many of the conclusions seem to have validity. Millennials and older "Xes" that I know, as well as those depicted in popular culture, socialize and consult with their parents, are skeptical of institutional religion, accept diversity, etc. The authors give some statistics for these and other conclusions, but without more complete data on the method and the subject pool, the conclusions are diminished.
One area I'm skeptical about is in the section on money. It is well documented that the Millennials have significant college debt and this is not even hinted at, suggesting that the 1200 member study group is skewed to either an upper middle class that has not had to borrow for an education and/or to those who have not had much education beyond high school. I'd be interested not only the demographics of the sample, but also the survey questions and if they really help define the Millennials on this topic.
The authors take continuous swipes at the Baby Boomers. For instance, the Boomers anti-authoritarian streak is negatively contrasted with the respect of the Millennials' respect for authority. It should be noted that the Boomers had reason to challenge authority. Authority structures were replete with institutional, de facto, legal and cultural racism and sexism. In the 60's and early 70's it was impossible for all but valedictorian Blacks and women to even consider medical or law school, to say nothing of the job markets they faced. The boomers made it possible for Millennials to face fairer authority structures. The Rainers say "The reality is that many of the leaders, Martin Luther King for example... was born well before the first boomer.." (p. 97) as though Silent Generation and the GI's were the ones who accomplished this.
A lot of their conclusions have intuitive validity if you know many Millennials, and the authors, being evangelical Christians, have no reason to skew their data since what they present it shows the Millennials trending away from the church; however, the lack of documentation, or even an index, and the unnecessary comments on the Boomers mitigate the value and authority of this book and its conclusions.