I haven't read JR's book yet only bec. the first copy I bought was a gift for a friend

. I plan on buying it for myself this week.
However, even though I haven't read it I have read lots or reviews and comments on it. I'm pretty sure that JR's book is an exposé on scientology, more than anything else. I don't think it's main focus is about what draws people into it, what is enticing or interesting or how it fulfills a person's desire for spirituality. What draws people into cults is not really the territory of reporters. It is more the territory of sociologists and psychologists. So, I'm not at all surprised the book left you with the question. In order to answer the question, you'd probably have to read lots of personal stories from people who went in, stories that explain what they thought it did for them.
Without knowing all the negative truths about scientology, a person who goes in with interest is only shown the good side of scientology. Once they start to see the bad in it, it may be too late, or they are so distracted by believing the lies, they hardly notice.
Like Wieber says, it is a hard question to answer even for us exes, but I guess I could give it a try. When I first entered scientology (and I was a young adult at the time), I thought it had the answers to life. I thought it could explain the workings of my mind, and help reduce or eliminate any and all problems that I was creating in my own life, based on the mental machinery that was holding me back. I thought it would help me recover from losses, from pain and suffering (very much a Buddhist goal btw). It taught me that I was a spiritual being with a mind that had infinitely more power than what was previously thought, if I could just free that power. It taught me that I could use that extra mental and spiritual power to accomplish any goal I wanted and to help others do the same. I thought it could teach me to understand my fellow man better than anyone had previously achieved. These are the promises of scientology and I definitely had faith in those promises. I took a college class on religion a couple of years ago and I realized that there were little bits of just about every religion woven into scientology. So I guess it has something for everyone.
To someone only reading critical information and exposés, scientology would seem like a religion without love. But there is love in scientology. One article titled "What is Greatness" is all about love:
L Ron Hubbard c. 1966 wrote:
The hardest task one can have is to continue to love his fellows despite all reasons he should not.
And the true sign of sanity and greatness is to so continue.
For the one who can achieve this, there is abundant hope. (...)
The real lesson is to learn to love. (...)
To love in spite of all is the secret of greatness. And may very well be the greatest secret in this universe.
Does scientology do for one what is says it can do? You have people who will say yes, and people who will say no. The hard truth is there are no legitimate studies that prove or disprove scientology's claims either way. All you have is personal testimony.
Do I think scientology did for me what I had hoped it would? That's hard for me to answer. Overall, no, it did not. Obviously, that's why I left. And I really left. I have not practiced scientology in any form probably since around 2004. The reason it did not is because the negatives came to so far outweigh the positives that any personal loss/gain assessment gave me no other choice. It was a slow road out and took years. Also, personally witnessing hardcore abuse for the first time in scientology, just prior to 2004 helped me to realize that scientology was probably a losing game. The curtain on scientology that hid the truth was peeling back long before I ever went on the internet and checked it out there or met critics or read an exposé, things I did years after distancing myself from it.
Anyway it was interesting to hear what your "take-away" was from reading JR's book. I have no problem with it. I believe her book is objective, and is the truth. I don't see the church of scientology lasting another generation. I also don't have any problem with individual people who still believe in it and who want to continue practicing it. But the institutionalized, corporate form of scientology is dangerous and has got to go.