Commenter Mix had assumed from that BT's title that it would be about what WoW zone you would craft in the game if you had a free rein to do whatever you liked. What a great question! Mix reckoned a zone that would be "an addition to the Goblin Starting Area or the Darkmoon Faire ... a rickety run down amusement park taken over by Gnolls or Troggs or Undead ..."
This sounds fantastic. I love the dark, eerie feel of the Darkmoon Faire -- in fact, I find myself far more drawn to shady, spooky zones than to happy, sunny ones like the plains of Mulgore. After massive overexposure to Firelands, I'm really not down with fiery zones, and I find forested zones a bit dull. The creeping blackness of the Sha in the Mists beta looks great, though; I like its incongruity in the lush world of Pandaria.
I also love snowy zones -- I like how your tracks remain in the snow -- so I reckon I'd want to create something like Darkshire but in a snowy area, with dark, greenish-blue tones and ghostly figures in a frozen world. It would be like Narnia might look if the Ice Queen had her wicked way!
What about you? If you could create a WoW zone from scratch, what would you make? The sky's the limit, and it definitely doesn't have to be inspired by existing zones. Go wild!