I like to imagine what would happen if Tolkien's Middle Earth and the history of D&D had whelped a hybrid mutant campaign setting. What would such a setting be like?
Firstly, elves wouldn't have been the movers and shakers over the milennia, as they were in Middle Earth. Far too pedestrian. I'd like to remove elves and replace them with the most ancient of D&D creatures: Mind flayers. It was the Illithids who were created first by Eru, the Illithids who went to Valinor, and a branch of the Illithids who rebelled against the Valar to wage eternal war for the Silmarils.
Second, there are no orcs. Orcs aren't D&D enough, and anyway, orcs are a corrupted version of elves, who don't exist in my Mutant Middle Earth setting. No, the dominant evil humanoid race is now the gnoll, created long ago by Melkor by fusing humans and hyenas.
Third, forget ents. Deep in the fastness of Fangorn forest there is now a great kingdom of myconids, hidden from the rest of the world and inaccessible to all but the bravest explorers.
In place of the Shire, there is a small mongrelman commune.
Numenor was formed by human slaves of the Illithids who rebelled and rose to great power before being stricken down by the gods for their impudence.
The haradrim are a decadent empire of gith, thri-kreen and half-giants.
Dwarves, of course, are Derro.
And Sauron is the most ancient and powerful of the yuan-ti, now attained demigodhood, while Mordor is the world's thickest and most fetid jungle. He has nine rakshasa servants, who ride on black dragons, and thousands of spawning pits for his yuan-ti minions.
Beneath the Misty Mountains lies a great labyrinthine dungeon scraped into the very roots of the mountains: the Temple of Elemental Evil...