Hellgate london was pretty much a diablo type game with upscale graphics and brutal combat.
I just can't see a diablo 3 coming out any time soon considering blizzard is working on a cutting edge mmo as we speak. Some say it will be worldofstarcraft. This actually makes sense when you think about the timing of everything with stacraft 2 about to be released.
The success of S2 and blizzards name means a mmo involving starcraft woud make an insane amount of money. They could also package a wow and worldofstarcaft price to own 2 accounts. Perhaps they would.give you a price break if you have an account for each game.