While it's probably impossible to avoid shallowness in presenting complex philosophical and religious systems in a novel, Vidal does a surprisingly good job of it: if you don't know anything about Buddhism or Confucianism or Taoism, then you could learn quite a bit about them from Creation. He's also careful to avoid any anachronistic traces of Christianity (although, in contrast with Buddhism and Confucianism, it could be argued that Zoroastrianism pretty much is Christianity), though I found the omission of a meeting with a Jewish religious figure a little surprising.
Although religious and philosophical ideas are at the core of Creation, they are never allowed to overpower the novel. There is plenty of historical (and particularly political) interest — poisonings in the Persian harem, the internecine feuds of the Greeks, the warring states of India and China. Much of this will be best appreciated by those who already have some knowledge of the history, but it isn't assumed. One of my friends described Creation as a "superior airport novel", but I don't think that is a fair judgement unless readability is a sufficient criterion for calling something an airport novel!