Here's a sample of Vance, from his The Green Pearl:
“None whatever!” declared the ex-priest. “I must admit that the issues possibly went a trifle deeper, and I may even found a new brotherhood, devoid of those stringencies which too often make religion a bore. I am restrained only because I do not wish to be branded a heretic. Are you yourself a Christian?”
The young man made a negative sign. “The concepts of religion baffle me.”
“This inscrutability is perhaps not unintentional,” said the ex-priest. “It gives endless employment to dialecticians who otherwise might become public charges or, at very worst, swindlers and tricksters. May I ask whom I have the pleasure of addressing?”
In his works set on other worlds, and in the future, Vance is also known for throwing out lots of imaginary cultures. In some books, he seems to put a new one in every valley, radically different from the one in the previous valley. In addition to bizarre clothing, food, and other customs, they often practice bizarre religions, and the religions are never spoken of respectfully. But, it is true that the clothes, the food, and the other customs usually aren't, either. It is as if each culture observed by his protagonists were in some sort of cultural zoo, observed through the bars, with the observer thinking that all of them are strange.
I have a web page summarizing much (not all) of Vance's writing, and emphasizing the different forms of vengeance often taken by his characters.
This page has an index of writings, associated with the Vance Integral Edition project, addressing the religious aspects of Vance's work, in particular whether or not he has been anti-Christian. Perhaps the most important of these is a long article by Paul Rhoads, entitled, as this blog post, "Is Jack Vance Anti-Christian?" Rhoads has an encyclopedic grasp of Vance's writing, which begins on page 15 of a .pdf document. Rhoads concludes that Vance is a neopagan, not a virulent anti-Christian (although some have said so), and that that aspect of his belief has been mostly incidental to his work. He points out that many authors, some undeniably Christian, have used hypocrital, or otherwise deeply flawed characters who claimed (fictionally) to be Christian, just as Vance has. I believe that Rhoads is correct on these points.
A taste for Vance is an acquired taste, but the man had talent, and has acquired a following.
Thanks for reading.
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On June 3, 2012, I modified the next-to-last paragraph. The most significant change was adding the title of the article by Paul Rhoads, which should have been included.