I agree that the randomness of Sacred is what makes it so fun. I'd definetly keep that but I'd also keep the sigle-player/multplayer aspect.
As for Diablo, it is a fun gam, and while the randomness of loot is not as random as Sacred, it's still a challenge to find set/unique items. Give it a try if youcan find a copy of it, preferrably Diablo 2.