This is why I liked the Wrath video:
It sets up some characterization for Imperius. He fights Diablo (briefly) without either really gaining the upper hand.
Even in the Act 4 intro, he puts up a pretty good fight despite facing a drastically superior foe (he draws first blood, and would have done fine if Diablo hadn't unexpectedly been strong enough to shatter his spear). Even getting impaled didn't completely stop him, and he's rushing back into the fight in the very next scene.
...he is pretty consistently portrayed in a fairly unlikeable manner, though. Short-tempered, impulsive, overconfident, and prideful. As an angel, he seems to be on the brink of Falling.
I really hope that redeeming or restoring the Angiris council comes up in the expansion.