Napoleon eventually lost a war against overwhelming odds when the entire rest of Europe turned on him.
I fail to see how this qualifies him as a complete failure. Unless you consider RE Lee to be “a complete failure” because he was eventually defeated by overwhelming force.
Napoleon was perhaps the greatest general and strategist of all time. Probably would have set up an empire over all Europe if not for the existence of that pesky English Channel. And of course his apparent inability to get beyond French chauvinism which eventually encouraged the growth of nationalism in the subject peoples and the disintegration of his empire.
A strategy is as good as its delivery. Actually, I don't think it was Waterloo that brought the end of Napoleon. It was his strategic mistake of invading Russia, which demoralized and weakened him & his army. Waterloo - that pesky English Channel :-)) was just the icing on the cake.