
The basic story line involves a long list of larger-than-life elements, which are pretty well known. Napoleon. Alexander. Etc.
Some other thoughts:
1. Zamoya thinks the criticism Napoleon took for starting the campaign late was unfair - felt he had no real choice due to the logistics around the horses and fodder. (Though this failed in the end, creating huge problems.)
2. Examples of Russian incompetence - political fallout as the Russian armies retreated. Kutuzov considered a national hero for various political reasons over time; Zamoya thinks he was ineffective.
3. Interesting information about the Russian army - 20-year hitches, pretty much everyone other than serfs bought their way out. The villages held a funeral when a serf went to the army because it was so unlikely that he would be seen again. Yet somehow they fought like dogs.
4. Marshal Ney unbelievably courageous.
5. The famous battle at Borodino - where the French win but lose. War and Peace based on this.
6. Moscow; fires.
7. The too-late retreat - I don' t think the author was gratuitously gory and violent in describing this, it plainly was just awful. Freezing, nothing to eat, both armies suffering mightily; the French would finally reach a destination and find out the logistics had failed again. Heroic bridge builders at river crossings (esp. the Berezina, where an unbelievable escape was achieved).
8. To some extent the peasants were armed and involved; this led to some agitation for political and social change; some of the military types ultimately became the 1825 Decembrists.
9. Alexander sold liberalism/reform to Europe. But things ended up very reactionary in Russia; and Prussia took a leading role in what much later became became Germany - also reactionary.
10. Stendahl part of the retreat - but early, lucky for him. He made it back to France. An incredibly small percentage of the Grande Armee survived.