Paul Vallely didn't come any closer to discovering why someone like Geri Halliwell might be interested in the Scientology religion, which was, after all, the stated aim of his visit to us. While it is easy to "skim" through a 600-page book and dismiss its contents, as Paul did, it takes a great deal more time and an actual personal interest to properly study the subject, apply it to one's life and see if it works the way it is said to.
As to those who have criticised Church of Scientology - what religion hasn't been criticised and persecuted? Witness Christianity.
Why were the Scientologists Paul interviewed able to give numerous instances of improving their own and others' lives with Scientology. In Scientology you think for yourself. You study the subject and apply it to your life, you receive spiritual counselling, and you see if it works for you.
While a great deal of Scientology is indeed "common sense", the subject as a whole is a practical religion, a summation of "workable truths" on which you can only really pass judgement when you have put them into practice and seen the results for yourself.
Fundamentally, Scientology is about the individual man or woman. Its goal is to bring an individual to a sufficient understanding of himself and his life and free him to make improvements where he finds them necessary and in the ways he sees fit.