If his power was turned in a more appropriate way, than he would be a great guy!
I would eventually change everything (alignment etc) if his offers in the dreams didnt end THIS way... no spoiling!
But he is a very decent villain! Although, without any AI patches, a very stupid one when the story comes to a fight
What if he finally "released my untapped power"?? I would be grateful! Unfortunately, all evil&powerful mages tend to pursue their own goals only... What a pity!