Christopher Hibbert writes in-depth, readable biographies, but he doesn't engage in much speculation on the inner workings of his subjects' souls. Napoleon: His Wives and Women (2003) is no exception. It's probably the best route, but I found myself wanting him to express opinions so I could argue with them or approve them as the case warranted.
This shouldn't be your first biography of Napoleon, since, as the title indicates, it focuses on his personal life rather than affairs of state and war. It assumes a certain knowledge of the major events and figures that a casual reader wouldn't have. But it's a good supplement if you're interested in the man and/or the era to get a detailed look at a part of Napoleon's life most histories barely explore. It didn't make me like Napoleon any better than I did going in, but I do feel like I have a fuller picture of his life and personality.