They were all murdered, weren't they? At the beginning of Oblivion, you can here this dialog; "My sons, they're dead."
"We don't know that, sire, the messenger only said they were attacked."
"No, they're dead... I know it."
Or something like that.
Well yeah, but if it weren't for the Mythic Dawn they'd all be alive.
Anyway, the Imperials aren't so bad, they want to do good. They set up schools for Argonians around the border of Black Marsh and they're trying to stop the Skooma trade that leaves many people on the streets and addicted in Elsweyr. They've freed the slaves in Morrowind and done a lot for the good of humanity.
They're just a little too pushy about some things. But Morrowind still held its culture very well, same with all of the provinces really. The only thing they've actually "taken over" is Leyawiin.
They're good at heart, and that's why I love 'em. I think the only culture who isn't generally "good at heart" is the Altmeri one. It consists of believing they are the "closest to gods", looking down upon the other races, and breeding to be more like the Aldmer.