Yeah it was a 4 person dungeon crawling game type. There was a bunch of classes with more restrictive skill trees then the main game,typically you joined a lobby then chose classes based on each other to make sure there were at least one of each of the 3 class archetype mage warrior thief to be able to unlock all treasure rooms.

They were not huge dungeons, but it was divided into 3 parts with varying objectives, with a monster rush at the end that was so intense on the higher difficulties that you would end with a loss unless you faught together more then half the time. Well besides a couple OP buileds if you got really good item drops.