Author Rowan Kaiser, writing for Gameranx, breaks down the plot holes and inconsistencies of Blizzard’s flagship game. I agree; the dialog is often atrocious. That said, complaining about plot in Diablo 3 is pretty well beside the point; it’s still an extremely polished, addictive loot game.
(As an aside, if you’re into gaming news you should be following Rowan on Twitter. Good source.)