I've never read the book (and I'm unlikely to), but from Wikipedia and the discussion afterwards it was a decent adaption of the novel, even through they dropped two of the five families the story was about. (The book follows a huge cast of Russian nobility, starting in the early days of the Napoleonic Wars, and ending shortly after Napoleon's disastrous retreat from Moscow.)
The production was divided into four films shot over several years (which gave the younger members of the cast time to grow up some). The first two parts had too much Peace for my tastes, but the last two parts more than made up for that, with Part Three featuring the Battle of Borodino, shot with 100,000 extras (Red Army soldiers). It was absolutely spectacle, about fifty minutes of chaos, fighting , explosions, guys on horses riding in all directions, and some really amazing camerawork.
The acting was very Russian, a lot of characters sitting around while the voice-over explained how they felt, instead of, you know, the actors actually acting. And the the final parts of the film there was a tendency for it to veer into being a Soviet propaganda piece, how the Battle of Borodino was one of the turning points of mankind and the victory (eventually) was due to the innate moral superiority of the Russian people (the WWII parallels were really played up). And all the peasants were rosy-cheeked.
Still, I'm glad I saw it, if only for the bragging rights. Only Joel once saw an eight-hour Hungarian film, so he's clearly still the winner.