This was absolutely fascinating. Let me count the ways!
It gains a coveted and rare five-star rating by actually making me change my mind about a few different items.
Let's start with the obvious. We've all the seen the Tufte "graph/map", and we've all been told that what this is supposed to tell us is that Russia is cold and the cold will kill your army. But I'd say the stronger message of this book is Russia is big, and that size, coupled with emptying the land, is what will kill your army. The first section of the book covers the march into Russia in summer, and that's just as miserable, just differently miserable, as the retreat in winter. And looking at the Tufte graph confirms this. There isn't a dramatic change in death rate in winter, more a constant death rate at every stage of the campaign from beginning to end.
So why these constant on-going deaths? To judge from the book, the underlying answer is chaos and disorganization. But again not in the superficial way you might think. There may have been logistics problems at the high level but it's unclear that they are especially important; much more important seems to be lack of MP's, lack of unit discipline, lack of self-discipline. Even on the march inward, let alone on the return, one gets the feeling that this is not disciplined hierarchical units but a mob of random individuals with few and random loyalties. Meaning that whenever resources (food, liquor, animals, etc) ARE encountered, most of the resources land up trampled under foot (along with a great many soldiers) in the chaotic fighting to acquire them. Likewise constantly deaths due to chaotic mobs trying to ford rivers, cross bridges, even wildly inefficient handling of fires and how to keep the maximum number of people warm with the given amount of wood.
I've mentioned in other places how anachronistic I consider the usual "theory-based" analyses of history that fantasize that, eg, the Crown of Spain or Catholic Church had much control over what various gangsters chose to do in the Americas, and I find it interesting (and not what I expected) that even three hundred years later, in what was supposedly the most organized army at the time, essentially the same still held sway. Napoleon could make plans, could even impose some degree of discipline, when conditions were just right and the scope of the project small enough; but when conditions were not right and the distances were the Warsaw to Moscow (let alone across the Atlantic Ocean...) it was very easy for the gangsters and psychopaths, the most violent and vicious, to do as they wished...
Another interesting aspect is the (lack of) social analysis. To hear the history books tell it (or Woodsworth with his "Bliss was it in that dawn to be alive") every random European from Lisbon to Vilnius had been given a new world view, a new theory of society and politics. Well, apparently the memo bypassed our author and pretty much everyone around him! He has very little interest in the people he encounters along the way. He's mainly interested in whether they are Russian (big trouble) French (allied but not friends) or German (maybe will help out, but still can't always be trusted). His primary comment (early in the book; I think we're in around Lithuania, maybe early Russia) on the common folk he meets is that they are less educated than Germans, don't work as hard or efficiently, and that this rot runs from the bottom of society all the way to the top (the schools/priests do a terrible job, the supposed rulers are venal and incompetent).
He does occasionally refer to people he meets as Jews, and I'd love to know more about what this signifies for him. It doesn't seem to be based on malice, more like Jew is almost a synonym for "trader/business person".
He has no opinions on the war, whether it was just or not, should be fought or not, is being fought badly or not. He goes where he is told, does what he is told, is glad that he gets to live through each battle or skirmish, and that's pretty much it. Likewise he doesn't seem to have any particular feelings for the Russians; no hatred, just an acceptance that his job is to kill them, their job is to kill him, and hopefully he does his job first. Likewise no special opinion regarding Napoleon, either as to his greatness, or in terms curses and anger.
Likewise no opinions on social relationships. He seems to like the major for whom he is a valet, and every time he re-encounters the major after they are split in some chaos or other, both seem happy. He has no complaints about the relationship between the two, or snide remarks about the major's not deserving whatever privileges he is awarded relative to his valet. In the cold of the retreat, he points out that no-one can tell officer from private, either in terms of clothing or behavior, so that, eg, both are equally scrambling wildly for access to food or fire; but that's all he says, no gloating that they have been given their come-uppance or anger that social betters are being treated so badly.
Essentially it reinforces my default position (and essentially provides another piece of evidence for Peter Turchin's Elite Overproduction thesis) that it's mostly the junior aristocracy/intellectuals/striving middle class that are obsessed with social relations and class structure; most people (ie peasants/workers/"the poor") actually don't give a damn.