Is he that bastard at the end of the second act (who's currently mauling my poor druid)? I didn't have any trouble with him my second time through.

When I was playing a barbarian (Ug was destroyed when I swapped computers, I'm still saddened to this day), I found jump attacks to be quite effective. Most online players use Pikes with barbarians, but I've always been of the philosophy that nothing says love like a big axe. Also keep your town scroll spell on a hot key so you can jump in, attack, jump out, and when you're low on health potions, make a quick escape to town to recoop. Usually a character is especially sensitive to one specific kind of attack, be it poison, fire, cold, or electricity, try and figure that out. Also, remember your war cries, and that if you're having trouble at level 50, you'll probably demolish him at level 51 or 52. You just have to take the time to level up. However, if you're getting killed with one hit, your armor or your vitality need MAJOR improvements.