Conclusion? It was completely and utterly fantastic.

Not counting the two intervals, it lasted for four hours, and the audience - including me - was riveted the entire time. I don't know any other director who can do that. I've sat through several indulgently overlong productions by directors famous enough to inflict that sort of thing on their audiences, but this is the first time I've hurried back to my seat before the interval was over because I was so eager to see what would happen next.
It helped that it was in a very small space, a former palace just off the Ringstrasse built in the late 19th century in the Renaissance style that serves as a rehearsal room for the Burgtheater (Austria's national theatre) and is also used for their smaller productions. This was the first time I'd seen the room stripped of the usual black cloth and flats, and it made for a brilliant setting. The set was just a series of grey tables put together to make one long table, lined with chairs, and behind it a model of the set. The director, Matthias Hartmann, came on at the beginning and explained with charming understatement that War and Peace was a tough text to adapt for the theatre, but they had thought they would see how far they could get, and since even with all the Burgtheater's resources they couldn't come up with a cast of thousands, they would be filming the little figures inside the model for the crowd scenes. It worked wonderfully.

They filmed other bits of the model, too, and projected them on screens or on the walls - this is the projection of the chandelier:

You can just see the model set underneath it, and one of the video cameras. You can see a bit of the room, too, and how they used the existing doors for entrances and exits, not with the usual black behind them, but with very visible lamps.
The audience was invited to look at the model set during the intervals, and it included not just the equipment for the sound and lights - which was all visible behind the long table on the real set - but also a tiny model of the model set, inside which you could just see an even tinier model model model set. And so, presumably, on
ad infinitum.
The tables were occasionally repositioned to indicate Prince Andre's father's country estate, and also served as a way of signifiying battles - the actors drummed on them with their fingers to create the sound of galloping horses, and banged their legs on the ground and threw them around for the battle itself. This is Napoleon walking through the aftermath:

He made a hugely imposing entrance, backlit through smoke, and then coughed as if the dry ice - not the "real" smoke but the theatrical tool of dry ice - was too much for him. The whole thing was done with that same lightness of touch, and a wonderful playfulness. the actors switched between dialogue and chunks of narrative, which they sometimes delivered as narrators and sometimes spoke as if it were dialogue. I don't think I've explained that very well. One example would be when Prince Andre loses patience with his wife and there is a long passage describing his internal emotional state, and the actor advanced on his wife as if he wanted to hit her, while shouting the lines as if these were things he was saying in the heat of a row, even though the actual words weren't doing that at all.
It's hard to describe acting, though, so have one final image instead (no, wait, there is one thing I can describe - how they played Anatol, the beautiful but dim philanderer and wastrel ("Anatol believed he had been created by God for the purpose of spending 40,000 rubles a year"). They chose an actor who was strikingly ugly but also so strikingly charismatic that his delighted smirking at his own beauty was both believable and hilarious. You had no trouble understanding how Natasha fell for him, and yet every time he beamed at his own prettiness you fell about with laughter at the incongruity.)
This is the scene where Andre meets Natasha at a ball. The screen revolved when it was pushed, and the actors danced with the screen between them, turning it rather than each other.

The page numbers were projected onto the top of the back wall, and the whole thing ended when the lights went dwon and the director came back on and said, "This is how far we got. Page number 1394 out of 1600," and then the various characters summarised - extremely entertainingly - what happened to them in the rest of the novel. When Natasha explained how she lost her "witchery" after marrying Pierre, Anatole said, "What a shame!" with such charmingly heartfelt innocence that the audience fell about, and then he got up and told us indignantly how he took it as a personal insult that Tolstoy cared so little about him that his entire death scene happened off-page and that he would NEVER forgive him.
It was magnificent, from beginning to end.