I read The Secret Lives of INTPs and its INTJ counterpart. The books share several of the same statistics, studies, and generalities so I have a similar review for both.
Anna Moss compiled a lot of research for this book. Roughly half of the book that doesn't deal with individual profiles is qualitative interpretation similar to what you will read on typology websites but with a narrower, topical focus instead of generalities that border stereotyping. Narrower topics include explanations of INTPs in relation to Asperger Syndrome, females and contradicting societal gender expectations, crime, habits in school, childhood behavior, relations to other types, political ideology, and comparisons to INTJs--yes, this is a small sample of the topics. The other half of the book that doesn't deal with individual profiles describes the same topics but mingles as statistics and case studies among the qualitative prose.
Something I certainly didn't expect when I started reading this book was the level of character analysis. Many of these people, some fictional and some real, I don't know, but I am impressed how deeply Moss investigates them and argues why they are INTP. Each person has a list of traits and in parentheses an indication of which dichotomies most likely explain those traits--I? NT? NP? A shorter list comprises of traits that argue against the character being INTP--E? NJ? After all, probably no one is 100 percent on the letter traits.
I read both Moss's INTJ book and INTP book because I'm INTJ but I found the INTP book first. I was two days into it before I realized there was an INTJ version. So why not read both? Behaviorally I fit the INTP description better so I figured I would still relate to and gain from the INTP book.
As an INTP, Moss included her own life as an example. How do three children, ENTP and two INTPs, prepare for Christmas? All is lost until ESTJ mother comes home. This is a lot like my mom and me: I like holidays, I just can't be bothered to dress up the house and do all the other festivities. My favorite quote by Moss is from her mom and about dealing with an INTP husband, INTP daughter, and ENTP and INTP sons, "It's like living with lawyers!" XNTP personality types are all about precision and they kept finding loop holes around Mom's rules.
One major short coming is Moss doesn't grasp the cognitive functions. She purposefully leaves them out other than for one section where she addresses why she ignores them. Her list of reasons mainly reword that there is no evidence of cognitive functions.
The thing is, there's no evidence that anything with MBTI is objectively true. It's not taken seriously by psychologists. MBTI and the cognitive functions are essentially an internal system of logic that has utilitarian value: it gives you skeletal notes for understanding how people process information. As someone who can't "read" people, cognitive functions have been key to improving my reading ability. The E/I, N/S, F/T, and J/P dichotomies is just swimming in the surface of the pool and cognitive functions are what you see when you dive. You can avoid more overgeneralizing, stereotyping, and confusing behavior for personality if you know where it all comes from--even if it's just a logical construct and not physical evidence.
"INTP" tends to be presentation: reserved (I), innovative and thinks well into the future (N), logical (T), and spontaneous (P). If you're slightly organized--as people often want to view themselves and will mistype because of it--you'll think you're INTJ. But we can learn to be social and assume that means extroverted--after all, it's another prized trait in our society, and F types can be logical. But if you look at the underlying mental process, you have Ti-Ne-Si-Fe: Ne absorbs potential realities and patterns in the environment, Si downloads the memories of Ne's observations, Fe acts--well known INTPs perform to improve society, and Ti both motivates and aggregates everything into an internally relevant and constant logical framework. The world has to make sense to an INTP.
There is much more to the theory and how the functions interact, but even the basic look at the functions actually tell you where a person is coming from when they say and do certain things. It's rich, it forces you to evaluate others more actively and critically, and it's fun if you like puzzles.
Another part mentioned is that a bunch of MBTI experts recorded adjectives they associated with different functions. This was a huge error. I'm not sure what researches conducted this. As I mentioned, cognitive functions and MBTI has an intricate logical framework--everything has a distinct meaning. Like how each of the 16 personality types come with stereotypes, this study asked experts to stereotype and apply generic associations to the functions. They redefined the functions in their own eyes and didn't incorporate the functions original definitions. Essentially, the results have no bearing.
Stripes are lines by definition. Let's talk about black stripes and gather some professionals to describe that stripes can be zebras, bar codes, on shirts, on cats, and evoke the feeling of anger. These attributes can be relevant in certain contexts, but they don't define that a stripe is a line and black is the absorption or absence of all colors depending on if it's made of paint or by blocking light.
Frankly, despite my affinity for the cognitive functions and Moss's lack of support for the argument that the functions don't matter, I didn't miss them. There was plenty more information to gobble up and the rest was reasonable and cited by interesting studies that did make sense.