I think a lot of RPGs from the 80s or so have a lot of similar properties. It depends exactly on what features in ADOM you are looking for most. Do you care most about difficulty? Complexity? Story or quests? Random dungeons etc.? Does it have to be rogue like?
For the other bit, closing the gate is saving the world. Ultra is something you do once or twice just to say you did it.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.