I already alluded to my "moment" in another thread.
In my initial playthrough, in the chaos of Helgen, I didn't realize I had any choice but to follow Hadvar, so my character did, and her sympathies were clearly aligned in favor of the empire, after speaking at length to Alvor and later others in Whiterun.
But my character fell under Ulfric's spell, Tullius was so immensely difficult a man to follow with any sense of passion, and Elisif was a shallow and weak character seemingly more interested in the luxury of attending Thalmor parties than in the hard work of leading a province through times of grave danger. My character gave away far too much to the Stormcloaks during the Greybeard's peace talks, and was almost accused of being just shy of treason for doing so. When you're basically a kid, and you're given such immense responsibility, and you are trying desperately to be fair, sometimes you can lose your way. She finished on the Imperial side, but with heavy and deep reluctance, and a very lasting sense of the utter and complete waste of it all: the loss of so many soldiers' lives, of course, but also, quite poignantly, the loss of a very passionate and exceptionally charismatic man who should have been able to put his irreplaceable talents to use to lead his people against the true enemy. A stupid, pointless waste, indeed. But that's war.
My character ended up hating the empire after that, and she gladly completed the Dark Brotherhood questline until the very end, when she met with her last contract. His demeanor and composure was enough to bring her full circle back to the very beginning...
It was quite an experience.