Napoleon and Wellington (Andrew Roberts, 2001) is a readable and compelling dual biography/military history...but only if you already have a fair amount of knowledge of the men and the era. If, for example, the names Salamanca and Borodino don't mean anything to you, you'll be pretty lost.
The book is almost a biography of reputations--what Napoleon and Wellington thought of each other before and after Waterloo, history's verdict on both and its accuracy or lack thereof. I agree with Roberts' assessment of their characters--that as much as each one's apologists would like to make them into contrasting types, they were actually quite a bit alike in their sheer arrogance, talent, and ambition. Napoleon was the more ambitious, sure, but who knows what Wellington might've done if absolute power had been an option for him. He did, after all, rise as high as an Englishman could in both military and civilian arenas, and seemed to think it no more than his due. Which, at least on the military side, it was, but that doesn't change the fact that Wellington was the very reverse of a humble man.
So, yeah, Napoleon and Wellington weren't exactly opposites. I still like Wellington a lot more--he was more humane and had a better sense of humor, for starters--and take the minority view that he was the better general of the two.
Anyway, this is a very good read for anyone with a fair amount of knowledge of the era. One caveat, though: unlike most of the nonfiction authors I'm drawn to, Roberts is clearly a conservative. I don't think his politics color his views of Napoleon and Wellington, but I have trouble believing the Whigs were as nigh-treasonous as he paints them. Must find a more balanced book on that particular topic...