I've never been a big fan of World Fantasy—you know, the sort of thing: a Tolkienesque World in which a cast of thousands has adventure after adventure after adventure. Kind of like Harry Potter, except more characters, and you have no guarantee that it will end at Book 7.
I usually run out of steam on Book 3 of just about any series. Yes, even Harry Potter. I still haven't finished the latest, although it appears to be better written than the one before. But, well, I read three books and then I read number four, and surely, that was enough?
With World Fantasy, I'm simply not that interested in flora and fauna. Many people like the idea of being exposed to a different world; they can hang out, tourist-fashion, and watch the scenery. But I prefer people—even in art, I prefer people, which is why I'd rather look at the Pre-Raphaelites than the Impressionists. Give me garishly colored knights any day over blurry trees.
Which leads us to the notable exceptions to my avoidance of World Fantasy:
C.S. Lewis is much more detailed in his science-fiction books, poetically so, but even there, the fascination seems to be less in creating a fully defined world than in dipping into a particular culture: anthropologist versus geologist.
Outside of these authors, whenever people tell me about a fantasy/World series that is fifteen books long, my first reaction is, "Please no." Which could lead me into a discussion about how much I disliked the soap opera-keep-you-endlessly-watching aspect of television shows, but I'll save that for a rainy day.