Save our wetlands!
Since people seems to be campaigning for just about everything else from the silly to the sensible, I thought I would strike a blow for the classic stuff. Some of my favourite crpg environments the last 28 years of gaming has been swamp and sewer levels. Things that spring to mind are the swamp lands of The Witcher (which was my absolute favourite part of that game) and a number of sewer levels in games like Baldurs Gate and a few older FPS games.
The slimy black mud that clings to your legs, all the way up to your armpits, the smell of rotten eggs, the "squish squish" sound of your boots slogging through waste and filth, what is there not to love?
Seriously, hand on your heart, would it be a role playing game if there wasn't a quest to go down in a sewer and solve the rat infestation? Come on, don't deny your roots!
Give me gloomy wet lands with a sense of being alone with all the dwellers in the deep, waiting to lash their rubbery tentacles around my legs and drag me to (not so) unexpected demise, the sense of relief when finally spotting a patch of dry land between the reeds with a copse of crooked and diseased trees where I can light a small campfire and chase away the darkness.
Just sayin', frogs and herons needs to live somewhere too!