The second I thought of destructable environments...
Who else thinks it wold be awesome to have a miner/digger/whatever class that can use shovels and stuff for faster digging and skills that allow for seeing through the upper parts of the ground and stuff that would bring digging into the battle? I personally would think it'd be awesome to be an annoying little mole, popping in and out of the ground and taking little potshots while mages try to blast me out of the ground XD