This is an excellent book with much original research. Out of the three schools of thought in early Christianity (1)literalist (Pistis); (2)joint literalist-gnostic; (3)Gnostic; Freke and Gandy are strong supporters of number (3), the Gnostic Christians.
Freke and Gandy attack literalist Christianity with venom, who they accuse of hijacking early Christianity which was eclectic and tolerant, turning it into the most totalitarian nightmare the world has ever seen. This included systematic destruction of the Gnostic Christian and Gnostic Pagan intelligentsia of their day and all their powerful knowledge they had gathered. Replacing it with mass ignorance and complete nonsense that was the beginning of the dark ages in the west.
The books great strength is that is unifies early Christian Gnostic thought, by identifying common themes that existed in all denominations of the Christian Gnostics, despite their individual differences. Describing the processes of hylic, psychic, pneumatic initiates and gnosis as the final prize for the initiate, in original Christianity.
The one big criticism of the book is Freke and Gandy's denial of the historical Jesus. Just because the independent evidence is weak for the existence of an historical Jesus, it doesn't mean he didn't exist as a person.
The totalitarian literalist Christians who seized power in the 4th century AD, may well have destroyed independent evidence of an historical Jesus fearing it would do damage to their ignorant vision, particularly if Jesus was a radical individualist and a Jewish Gnostic, such as an Essene or a Therapeutae initiate and not the totalitarian figure the new powerful Christian church wanted to falsely portray. Freke and Gandy don't address this argument.
Also another criticism is that Literalist Christian may not have always been this total monster that Freke and Gandy portray. Because Literalist offered a sense of community, self-belief and faith, that gave its followers in face of persecution, an intuitive sense of strength in unity before the 4th century AD. Literalist Christians were a solid movement, while the Gnostics Christians were no match, being only a loose network. Only after the 4th century AD and the seizure of power by the literalist Christians, one could argue, the democratic literalist vision was hijacked and twisted by these new, sinister, totalitarian literalists who seized power for their ignorant uses and plunged the west into darkness for 1000 years, before the Reformation restored some sanity.
I am sure Clement of Alexandria and his pupil Origen would have agreed with much of the above paragraph and that is why both these early Church Fathers were supporters of the joint literalist-gnostic school of thought. This expressed both the literalist exoteric outer mysterious (historical, the community and faith emphasis) and Gnostic esoteric inner mysterious (mythological, the individual and self knowledge emphasis), which the writer believes was the framework of original Christians, before the church split in two, with the literalist and Gnostic factions disastrously going their separate ways in the 2nd century AD.
Despite these criticisms get a copy of this book now. This is an important book in the "Jesus Debate". It shows how easily a philosophical religion of inclusive, democratic freethinkers with "unity in variety" and a "freedom to question" as their message can be hijacked and turned into the control religion of the exclusive, authoritarian personality (see your psychology books), with "them and us" and a "duty to believe" as their message. That is what happened to Christianity and many of today's Christian denominations are a misguided product of this.