As every human being he had certain flaws, as far as I remember well what I learned myself a few years ago? He had a good start with tactics, but with every battle he was getting more and more arrogant. The summit of his arrogance was at Waterloo, when he decided to take a nap, as in his own consideration the battle was already won and there was nothing to screw up, so he gave command to one of his lieutenants. Well, guess what. Cavarly chasing infantry behind the hill - shit, it can't be trap, right? Nooooo they're so beaten. Oh, carronades are standing there OH SHIT.
I remember also that he was known for being rather impetuous and bad tempered.