I was very surprised to see that no one has reviewed this on Amazon yet. I was also surprised to come across the copy I bought recently, it having passed me by when it was published. But having thought about it I do remember reading what I now realise must have been an excerpt from the book in the Sunday Times (probably) which concerned his views on the lesser, and NOT all powerful, God as the 'Great Artist', just the sort of God a great novelist might conceive. What I didn't realise was that there was a whole book with a much bigger cosmogony.
Mailer's book is just as readable as Dawkin's but far more original and significant in itself. Obviously no one who in interested in understanding Mailer's novels can afford to ignore it because this is the philosophy behind them, certainly those written since he was 30 and realised he wasn't an atheist any more. Essentially it's a free thinking attempt to work out a rationally coherent theology - that is to say one that is internally consistent and also anchored in his experience of life - making use of the suggestions that might be found in the various traditions. If you rejected religion and God on rational grounds, as for example I did myself at 14, then this should serve to convince you that it is possible to give an account of a possible theology that cannot be rejected on these grounds and that you might need to think again. Perhaps your idea of what God has to be was too limited in the first place. In my own case I found my own way out through Pantheism and then gradually found I needed to think about Buddhism, Neo-Platonism and eventually Gnosticism. The book is couched in a question-and-answer format with an interviewer and so is presented in easy to digest semi-labeled chunks. He is very strongly Manichean although the relation between his artist-manager demi-urge and his evil angels is a complex one, and reincarnation plays a big part in his cosmogony. At the same time I would be surprised if anyone didn't find plenty of common sense and intelligent insights of every kind.
Read it as a great speculative science-fiction if you like, in the spirit of Harold Bloom's 'The Flight To Lucifer: A Gnostic Fantasy', or as a philosophical thought experiment - if there were two Gods or gods how might the more managerial and fallible one behave?