Instead of having a dungeon with 100 levels, why not have something which could fit into the Diablo universe.
I'm talking about a portal to hell, a hell rift.
Here's my idea:
Have a few different maps (to suit different parts in the game, eg: Tristram, cathedral, caves, act 3 Bridge, Heaven/heavens hell rifts, etc.) either randomly generated or fixed positions, but different maps could mean different strategies. you could have one open style map where the demons could surround you and you have to stick together to fight them off, or have a hap with a choke point where you could set up a defense with tanks at the front and glass cannons at the back.
Monsters would come out in waves maybe with an elite to "lead the charge" , and every 10 waves or so a boss would appear, and every wave the monster difficulty would increase.
Bodies would disappear almost immediately in order to reduce screen clutter, white items would be non existent, and at the end of every wave maybe an item would drop, 75% to be a blue, 15% rare, 5% set, 5% Legendary (on the later levels, in the early levels it would be different.)
What do people think?