I’m pretty sure I’m in the minority on this one, but I happen to really like novels set in RPG worlds, as a general concept.
That’s not to say that I think all RPG novels are inherently good. Just look no further than the hated Rose Estes Greyhawk books from the mid-1980’s, with all their explicit furry-sex, magic daggers killing demigods, and other inanities. But some novels are quite good, both as novels, sourcebooks for the settings in which they are set, and as guides for how some aspects of those settings can be used.
It should come as no surprise that I’m a huge fan of the Gary Gygax “Gord the Rogue” novels, although their utility as sources of information regarding the World of Greyhawk drops as you reach the last couple of books (mainly because Gygax had left TSR by that time, and the books depict the destruction of that setting). But I was also a fan of the Forgotten Realms books, at least the early ones, and, at the risk of really blowing my OSR cred, I liked the Icewind Dale trilogy when it first came out. The Dragonlance novels were excellent introductions to the setting as well, which should come as no surprise, as the whole setting was built around the fulfillment of novel-like story-arcs.
Where RPG novels don’t work is as tools to “advance the setting”, which is a practice with which I’m not happy no matter how it’s done. But to flesh out a setting, I like ’em, as long as they’re halfway well done.