It wasn't all that bad, but I'll have to say it wasn't all that good, either. I usually love spy themes, especially if the story is set in either the American Revolution or - like in the Civil War. I try to picture myself in the h's situation. If I had suffered a lot of losses in the war and was dedicated to a cause I felt was right (though in my case, it would have been the Union), I'd want to do what I could to be of service. However, if my heart got involved, I'd take a step back.
That's what Susanna should have done, once she admitted to herself she had fallen for Mitch, especially since she put him in danger, it wasn't just a matter of getting info anymore. It's understandable why this story had to stretch out for several years after the war, because forgiveness couldn't come quickly. (In real life, I doubt very much it would have happened at all.)
Mitch, however, has to accept his share of the blame, an officer with heavy responsibilities has to be continually on guard, not act like a lovesick teenager. In a way, he deserved to be made a fool of.
What I really think, is that if this book had been written back in the 80's or 90's, it would have been a lot better. Back then, authors wrote with a flair for drama and passion that's lacking today. The characters seemed to lack any real feeling, even the sex scenes were cold and clinical, rather than hot and steamy.
It was just missing too much.