Before getting on with my criticisms, I would like to say that I actually like most of the philosophy (not the religion) in this book -- which really is too say little more than that I had come to similar conclusions myself. (A statement I've also made of Stephen Mitchell's "Tao Te Ching" -- a book LeVay would probably not have cared for.) LeVay sometimes takes things litte too far, but only a little.
Having said that, I might note that, when it comes to logic, LeVay is not as faultless as he is often creditted with. He is only slightly more logical than good Christian, Pagan, and Eastern theologian. Often, there are (il)logical jumps, inconsistancies, rhetorical word-games, and babbling circumlocution. Also, he makes some techinical errors is the trivial he uses to eximplify his view: e.g., the English "Devil" is derived from the French "Diable," which comes from the Latin "Diablus," and ultimately the Greek "Diabolos," and is not related to the Hindi "devi" as LeVay states. On factual maters, I would guess LeVay to be 60-70% correct. All this is still at least as good (probably better) than most religious works, however.
LeVay's biggest short comings are in (1) justifying a Satanic religion, and (2) characterize human nature to narrowly and inflexibly. On the first mater, LeVay does try to answer the question of why he proposses a Satanic religion rather than just practical materialism, but his justification is basically a lot of babblement and he talks around himself. (As an atheist, I see no reason for having religion, and LeVay's answer was hardly satifying, let alone convincing.) On the second mater, LeVay barrows a lot of (now held doubtful) Freudian doctrine, and further assumes that there is a very large, encompassing human nature, which is virtually invariant. This second problem, the failiure to fully realize human bio-cognitive diversity leads to a fair amount of judgementallity. LeVay assumes any who don't fit his mold are "repressed" and dishonest, and holds open contempt for such as "liars." I have found that most Satanists I've talked to are terribly self-righteous and judgemental (in there own way), and this may be the root of it all. (This is not to say all Satanists are so narrow -- but this seems common, and makes sence if LeVay himself encoded it.)
Finally, I want to note, since its is frequently claimed, that Satanism is not a from a Christianity! (Nor is it Pagan.) It is obviously a religious movement unto itself, and not part of Christianity anymore than Christianity and Islam are part of Judaism (or Judaism part of ancient Paganism). This "Satanism=Christianity" rhetoric may be a fun way for Pagans to slam both opponents at once by comparing each to there own worst enemy -- but an objective reading of The Satanic Bible shows that Satanism (for better or worse) is something unto itself.