Someone else said it already in this thread, but the game is filled with morons. The emperor is Belial? Oh no! Kulle is going to betray you? Oh no! Adria is suspect? Oh no! Everything is extremely predictable, but somehow not for anyone involved in the story. They drop hints about absolutely everything.The Angels apparently chucking Diablo's body down to Sanctuary despite the Black Soulstone still being in it is the stupidest shit imaginable. Adria will probably recover it in the expansion and resurrect Diablo with it. Maybe Imperius will attempt to destroy Sanctuary and the Prime Evil with it.
And playing as Witch Doctor the 'spirits' they talk about tip them off about all sorts of shit, but never anything mentioned above.