Wellington and Napoleon: Clash of Arms 1807-1815 (Robin Neillands, 1994) is a quick read, light on the details, at right around 250 pages. I've read books on the Waterloo campaign alone that were significantly longer. But that doesn't mean it's a useless read. It's just a snapshot of the big picture, which is a useful thing to pull back and examine on occasion. It's easy to get lost in the forest of details when you're reading full-length books on individual battles and similarly exhaustive histories.
And one benefit of this book is that since Napoleon and Wellington never actually fought against each other prior to Waterloo, Neillands has to go back and forth between the separate fronts they fought on beforehand, which shows how they influenced each other--something I think is often neglected in books that focus on one man or the other.
Anyway. Every ranking of all-time greatest generals I've ever read puts Napoleon ahead of Wellington. I feel like I must be missing something obvious that I'd know about if I were a reallyo trulyo military historian instead of a self-taught wannabe military novelist, because I just don't see it. And not just because Wellington won their single meeting--Waterloo was a special case in a lot of ways, and I don't think showcased either man at his most brilliant. And I'm not denying that Napoleon was brilliant. I just think that Wellington was the more flexible and adaptable of the two. There wasn't as much of a pattern to his battles, at least from how I interpret what I've read.