"If Napoleon had remained emperor of France for the six years remaining in his natural life, European civilization would have benefited inestimably. The reactionary Holy Alliance of Russia, Prussia and Austria would not have been able to crush liberal constitutionalist movements in Spain, Greece, Eastern Europe and elsewhere; pressure to join France in abolishing slavery in Asia, Africa and the Caribbean would have grown; the benefits of meritocracy over feudalism would have had time to become more widely appreciated; Jews would not have been forced back into their ghettos in the Papal States and made to wear the yellow star again; encouragement of the arts and sciences would have been better understood and copied; and the plans to rebuild Paris would have been implemented, making it the most gorgeous city in the world."
Some arguable points, but Napoleon was... shall we say, capricious. It seems naive to think that all this would have happened the way it's put there.
Still, it makes for fun speculation. If you like that, you should read Creasy's "15 Decisive Battles in the History of the World," at least if you don't mind a bit (well, more than a bit) of Anglocentrism. There's a lot of this "if things had gone the other way" stuff and it's great conversation fodder.
Also, Hugo's narrative of Waterloo in "Les Miserables" is wonderful and worth reading if you are at all intrigued.