The story is told in a classical romance style, with the point of view moving back and forth (without the head-hopping, thank goodness) that you'll find in most romance novels. That aside, the main characters don't spend all that much time alone together. The love scenes are sweet, believable, and mercifully brief compared to the chapter-long sex scenes that seem to prevail these days. The characters think about each other a lot and interact, but the setting — the American Revolution — drives the story instead of the angst of our two lovers. In fact, I would say these two are about the most level-headed hero and heroine I've ever met.
I loved the history in Mistress Firebrand. However, I could see how someone without some understanding of the America Revolution might get a little lost. I actually got a bit lost in all the references to theatrical plays, but since I understood the history that drove the story I was able to gloss over it. Others might want to have Wikipedia standing by.
The book was well researched, although I suspect the author only needed to fine-tune the details. I also loved that she never had one side or the other totally be "the good guys." I did like that she portrayed Washington as a good guy and not Burgoyne, but she didn't gloss over the horrors of the conflict and what both sides were willing to do to each other.
All in all, a great read.