in no particular order:
Baldur's Gate 2 + addon
Might and Magic VII
The Bard's Tale (for the C64)
(it's REALLY hard to not have honorable mentions)
And for the record, hack-and-slash is the building block of ANY RPG, because most RPGs require you to kill rats, then orcs, then goblins, then trolls, then giants, then dragons, etc etc etc to build your characters up. To dismiss something like Diablo II as not being an RPG based upon its game sytle is a fallacy; to dismiss it because there is only one way to finish it is as well (because Ultima IV, THE grandaddy of all RPG games, can only be finished by a 'good' character).