JohnSnow
Hero
Jürgen Hubert said:Planescape: While based on standard (at the time) D&D cosmology, it diverged very far from the common fantasy tropes.
Spelljammer: Again, too wildly divergent from standard fantasy to gain mass appeal (in my opinion, they should have emphasized parallels to the historical Age of Sai much stronger - including a "default setting" with multiple "core worlds" similar in culture to the powers of Europe and a "colonial rim" similar to overseas colonies of the former.)
Dark Sun: Again, very different from any tropes and stories most people are familiar with.
The problem with these settings is that they're not even "Medieval Fantasy." All three are total "gimick" settings, relying on nothing but their central premise.
By contrast, Eberron is still "medieval fantasy," albeit with some very fantastic elements overlaid. Based on all reports, it's a quite successful setting. Another example of this type of fantasy that's doing very well is Monte Cook's Ptolus. Some other examples of settings like this include Zakhara or Mystara, where the fantastic is quite a bit more prevalent than in a setting that's more like "medieval europe plus monsters and fantasy races."
The latter is perfectly doable in D&D, but actually bringing the fantastic into the society (in a way that isn't just a ripoff of modern technology powered by magic) is actually a challenge worthy of the efforts of professional game designers.
If you want The Lord of the Rings, the DM's work is already done. But a setting where the magic is incorporated in a way that's logical without being silly is actually interesting.