People consider it a task reading any Tolstoy book, but when they realize Tolstoy's reasons behind writing so much, they shall simply fall in love with his works. In War and Peace, you may ask why Tolstoy included so many scenes of so many characters. The last philosophical epilogue that many people choose to skip provided me with some answers. Tolstoy felt that there were innumerable causes, time and external factors to analyze before judging a person's actions or an event. His scenes are branched out only to emphasize this very point, that a person can't be judged as good or bad by just regarding one deed of his/hers. Take Natalie's elopement for instance: in the book, we sort of anticipate this impulsive tendency of Natalie through her internal thoughts, her family's similar traits and her failed romances with Boris and Denisov. This not being clearly mentioned in the movie, we are forced to think Natalie tries to elope only because she was unwelcomed by Princess Marya and Count Bolkhonsky since their encounter precedes the scene at the theater. Tolstoy the writer had the freedom to extend his book as much as he wanted to justify his characters' intentions to an extent, while King Vidor the filmmaker has to consider many factors while making War and Peace, the most important being to make his work a box office hit. Thus, in spite of being fairly impressive in bringing the book to screen, Vidor's War and Peace isn't able to capture the nuances that the genius Tolstoy could.
The runtime of War and Peace, despite stretching a generous 210 minutes doesn't manage to do enough justice to many of its events, especially the arc involving Pierre's relationship with Helene, which had to be deliberately stretched 'without' the presence of the characters together in order to emphasize how pathetic and disconnected their marriage was, but isn't. Through this disconnection, Pierre's feelings of attraction and pity towards Natasha automatically increased in the book but since the scenes in between the rare encounters of Pierre with Helene can't be stretched too long in the movie, there isn't enough of the latent passion within Pierre towards Natalie as in the book, especially when Pierre comes to console Natalie after her failed elopement (in the book, Pierre is so moved by her plight he immediately falls in love with her).
Or take Napoleon's accession and fall; in spite of Herbert Lom's sincere performance as the pompous, arrogant tyrant, we don't feel the aura that a war and its aftermath should create because Vidor limits the number of characters, thus not emphasizing Tolstoy's statement that in a war, there are so many forces working together. The countless negotiations and treaties, the faulty calculations and wrong assumptions by the various argumentative generals and the pawns in the form of millions of Russian and French soldiers was so comprehensively and exhaustively charted out by Tolstoy, readers simply felt overwhelmed and overawed by the gravity of the situation. Vidor plays safe, partly because its 1956, partly because of his direction style, partly because of the screen duration, partly because of budget limitations and partly because it's Hollywood.
Pierre's development is quite disappointing; while in the book, he undergoes a sea of change that teaches him that 'the kingdom of God is within oneself', in the movie he (and Prince Andrei) seem secondary to Natasha Rostov. Instances that are supposed to cast a deep impact on Pierre such as the arsonists' execution scene are hastily finished with, and without the inner voice that Tolstoy persistently gives to his characters, Pierre just seems like the same old albeit wounded Pierre after the war. And the Hollywood like resolution was thoroughly unsatisfactory; remember how the intuitive Princess Marya realizes Pierre's feelings towards Natalie and agrees to have a word with her in the book - that anticipation is missing in the movie. John Wayne is miscast indeed as Pierre, but more to blame are the dialogs which do not bother capturing the complexities of Pierre's nature. Brando, the method man could've done much more had he been provided the geeky spectacles of Pierre - he would've demanded for a fat suit to get into Tolstoy's version of the character. Mel Ferrer is in the same boat as Wayne; the issue with him is that his mouth speaks more than his eyes. Not in the case at all with Audrey Hepburn as the spirited, caring and spontaneous Natasha; Hepburn outshines everything else in her scenes with the deeply expressive eyes and her whole body language. The ballroom scene is perfectly played by her and it is exactly how Natalie had been written in that chapter in the book.
The audio recording (rerecorded at the studio) is, as you may have heard from many other viewers, bad and some good dialogs sound flat and not in synchrony with the actors' lip movements. The visuals shine but personally I was looking for something darker especially during the war scenes - the murkier the war is, the more we connect with the characters' pains. Costumes at the soirées are better suited then those at war, but I guess Vidor wasn't aiming for too much realism. In the end, War and Peace the movie is a hit or miss affair - it hits whenever Hepburn turns up, stays afloat most of the time and misses at doing complete justice to Tolstoy.