There are several reasons why I'm not altogether sold on Newton's work. For one thing, it is well-known that subjects under hypnosis have a tendency to confabulate -- to make things up in order to please the hypnotist. (See D. Scott Rogo's book The Search for Yesterday for a detailed discussion of confabulation and the related topic of cryptomnesia.) Newton asserts that people in "deep hypnosis," unlike most hypnotic subjects, cannot confabulate, but he provides no evidence to back up this claim.
One of Newton's arguments in favor of the veracity of his subjects' accounts is that they tend to agree with each other. But he also says that many of his patients approached him after being recommended by friends who had undergone the therapy. It seems likely, then, that some patients came into the process with preconceived notions of what to expect, which could explain the relative consistency of the reports.
From the fairly brief excerpts of the sessions presented in Newton's book, it's hard to know how much he may have unwittingly led his patients. Sometimes patients do contradict him or argue with him, but only over minor details. It is at least arguable that the general overview of the experiences they report is constructed out of conversations with Newton's other patients and Newton's own expectations.
Another issue that arises in hypnosis is ESP. In the 19th century there was a great deal of interest in a possible connection between the hypnotic trance and telepathy. Experiments done at the time seemed to indicate that people who have been hypnotized demonstrate enhanced telepathic abilities; in other words, they are more receptive to other people's thoughts. I can't help wondering if Newton's patients are picking up his own thoughts and simply reciting them back to him.
Although Newton says he has obtained many descriptions of past lives on earth, he does not seem to have made any effort to corroborate these stories. In one case recounted in Journey of Souls, a patient recalls a life in the 19th century as an Oklahoma prosecutor named Ross Feldon, who committed suicide at age 33 (p. 57). This is the kind of thing that could probably be checked by poring over historical records, but Newton makes no mention of trying to confirm the account.
When it comes to the "life between lives" reported by so many of his patients, there is no way, even in theory, to empirically confirm the stories. We are left having to compare them to accounts provided by near-death experiencers and mediums. Though there are some areas of overlap, there are also significant discrepancies. The life review, described in so many NDEs, is absent from Newton's reports. His subjects say they talk about the events of their earthly lives with their spirit guides, and they may look through books that contain moving images drawn from their past lives, but there is no description of any holographic reliving of one's life.
There also is very little discussion of what has been called Paradise or Summerland -- the earthlike environment of the afterlife, featuring gardens, meadows, houses, birds, etc. Some of Newton's subjects do recall studying in a beautiful library, but for the most part the afterlife environment, as they depict it, seems to consist of blobs of color (which are souls) zipping around in a rather abstract geometric setting. It reminds me a little of the old sci-fi movie Tron.
Information that comes through mediums usually indicates that the topic of reincarnation remains controversial even among the departed, with some of them expecting to be reincarnated and others believing differently. But if Newton's accounts are to be believed, there couldn't be any confusion in the matter, because the newly departed soul is almost immediately reunited with its friends from other lifetimes, and proceeds to spend nearly all of its time in heaven preparing for its next incarnation. There is really no way to reconcile these contradictory accounts, so either the channeled information is wrong or Newton's information is wrong (or both are wrong).
One thing that makes me a tad suspicious about the claims elicited by Newton is that his patients become evasive or uncommunicative when difficult questions are put to them. Newton interprets this as meaning that they are "blocked" from divulging certain details, but another interpretation is they've been confabulating, and when they reach a point where their imagination fails them or they aren't sure of the answer a therapist wants to hear, they clam up.
It may seem that I'm being overly critical. If so, one reason is that I'm not particularly inspired by what I've read so far. At this point, I'm finding Journey of Souls to be a rather blah and uninspiring vision of the hereafter. I'm not sure I want to be a blob of color drifting among other blobs, trapped in an endless cycle of earthly incarnations punctuated by tedious classroom lessons. As far as I'm concerned, the visions of the afterlife presented by Swedenborg and later mediums, as quaint and old-fashioned as they may seem to some, hold considerably more charm and appeal.
This personal preference on my part doesn't mean Newton is wrong. It does mean, however, that I will need to see a lot more evidence before I'm convinced.