I'm not fully versed in Diablo lore and all of the worlds areas, but I suppose if I had to choose a place, going back to the swamps from Diablo 2. Is there any place else that would be worth checking out?
Maybe not creative or original, but I feel that is the terrain type most lacking and suitable for a new act. --- Don't think of it as deferred gratification. Think of it as immediate suffering. - Peter Bellamy
In some part of act 3, a messenger comes and says some king from somewhere (Westmarsh?) won't send men to battle imaginary demon lords etc.
I want to go there to burn that ****ing city to the ground. My hero can be corrupted like other heroes from the lore or whatever. --- "Careful? Was my mother careful when she stabbed me in the heart with a clothes hanger while I was still in the womb"