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.
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.