John C Wright's "eschaton sequence":
Count to a Trillion
The Hermetic Millennia
Judge of Ages
Architect of Aeons
The Vindication of Man
(and one more to come)
It's a combination of hard sci-fi and space opera, based around one essentially immortal character (and his rival, and his girl) carrying out a mission over tens of thousands of years. Mind-blowing scale and yet there's a romance to it.