It's definately doable. Just gotta have a good merc.

Getting through norm/nightmare on a character is easy. Once you get to hell, the real challenge begins. You can't just fly through it like you do in norm/nightmare, you have to stop every once in a while to just level up, gear up, level your merc, etc. I can't think of any character that absolutely could NOT beat the game in hell solo. Some are easier than others, and sorcs are one of the easiest by far. I would wager, assassins, druids, and paladins would probably be the 3 hardest characters, but that's assuming you don't have the leetest gear that you transfered over from another character.