LogFAQs > #896891672

Duriel is a poorly designed boss, where in the single player mode (ie, where you have to actually do it yourself, not just tag along) several common builds simply cannot win at the levels you'll be when you face him. He's not difficult in a way that makes you think or fight with perfect precision. He's difficult because he's cheap, with a fast-charging stunning attack in a tiny cage designed especially to his strengths.
If you're playing a bow amazon, the build the game most expects you to play if you're a 'zon, you should not have to ditch the bow entirely and take up a javelin/spear just to get past Duriel. And yet....that's the easiest way to beat him in that situation.
Ultimately, Duriel's a "test" of whether you have enough strength for a belt w/ 3 or 4 rows of potion slots or not. That's about it.