Comments on recent entries suggest that there is a need to clear something up about fantasy settings.
Look at the following spectrum:
Any fantasy setting can be placed somewhere on that spectrum. Across one dimension it serves, of course, as a proxy for quality. Urth is a powerfully rich, unique and dense setting and the books Gene Wolfe set there are wonderful. Krynn is derivative and the Dragonlance books are not very good.
But that is not the dimension that interests me. What I'd like to emphasise instead is that Urth is a very singular setting - unique, indeed, to the brain of Gene Wolfe and probably unreplicable (except in weak, uninteresting pastiche) by anybody else. Krynn, on the other hand, is a shared one. Yes, I suppose Maragaret Weis and Tracy Hickman came up with it. But it is founded on conventions that anybody who has read a fantasy book will recognise and which are, to a large extent, common property to fantasy fans. (And this is indeed why so many people have contributed to the Dragonlance series' over the decades without really changing the books' mood or character appreciably; Volume 51 of Kender, Gully Dwarves and Trolls is basically the same thing as Dragons of Autumn Twilight - different varieties of cheddar cheese.)
When it comes to novels, I want everything clustered to the left hand side of that spectrum. This is probably also true of those RPG settings which I know I will never play.
But when it comes to actual gaming, it is important that settings lean towards the right. Not all the way, by any means. But at least part of the way there. This is because RPGs and novels are fundamentally different things. Reading a novel is all about becoming involved in the singularity of the author's vision - or, at best, co-creating that vision in one's own mind and imagination. There, distinctiveness is what really matters, and singular settings are therefore best.
Playing an RPG, though, is about running a successful game. It's not chess, football or boxing, but ultimately it is still about communal fun. Sitting down at the table, the players are not simply engaging in exploring the DM's beautiful and unique creative product, but actively contributing. This requires them to have a certain footing on the same ground - to be deploying certain assets of shared property. The setting they are inhabiting does not have to be as derivative and bland as Krynn, but it has to take at least certain assumptions for granted in order for there to be long-term success.
Tekumel is perhaps the classic example of an edge case. It is a unique setting, for sure, but it perhaps has enough of the shared furniture of D&D - the quest for gold and XP, the basic system, the core conceit of exploration/dungeoneering/questing - to make it gameable. With Yoon-Suin I suppose I was aiming for something slightly to the right of that.
Another reason for preferring game settings to be on the shared end of the spectrum (rather than the singular) is simply that what happens in a game tends to do extreme violence - literal and figurative - to the setting, and the DM's tolerance for that happening if his game is set in an environment like Gene Wolfe's Urth is probably much lower than if it is set in a place like Krynn. In this respect, a setting like Krynn, the Forgotten Realms, and so on is a bit like an ABBA song - even if Piers Brosnan is singing a cover version in a crappy movie, it still kind of works on its own terms because those melodies are almost part of our cultural heritage at this point. But nobody wants to hear him singing Captain Beefheart.