McQueen is an auteur known for his honest and brutal direction, and he keeps filming when others would shut the camera off or look away. While making the picture that much more difficult to sit through, his steadfastness greatly elevates the emotional impact of the film. It's a must-see, if only for educational purposes—just as 'Schindler's List' is used to teach about the Holocaust and 'Milk' about the struggle for gay rights.
I'm not trying to compare the events depicted in this film with the events depicted in those I just mentioned, all I'm saying is that they are all equally important in portraying the reality of their respective situations. There is a moment in '12 Years a Slave' when, as a form of punishment, Northup is hanged by his neck, the tips of his toes just able to reach the ground below him. The camera stays on him for a few minutes. It is silent, and all you can do is listen to him struggling for breath.
This is one of the more disturbing moments in the film, but not the worst. Eventually, Northup is sold to Edwin Epps, a short-tempered and impulsive plantation owner portrayed by Michael Fassbender. He is by far the most villainous and terrifying character in the film, and Fassbender brilliantly captures his mood swings and tempestuous personality.
It is Chiwetel Ejiofor, however, who steals the show. He brings so much life to Northup, and completely disappears into his characters. He is able to depict so many deep levels of emotion, while also bringing dignity to a man who was unwilling to let anyone take away his will to "live" rather than just "survive." Additionally, Lupita Nyong'o, in her first big film role, is mesmerizing as Patsey, and hardworking and desperate woman, and the object of her master Epps's attention. She is hated by Epps's wife—masterfully played by Sarah Paulson— and most of the more dramatic moments in the film revolve around her character's tragic story.
If I have one complaint, it's that 12 years do not seem to pass by at all, mainly because none of the characters substantially age. Also, Brad Pitt is thrown in for ten minutes to depict a kind-hearted abolitionist, and while he does a good job, it just feels like Brad Pitt on a slave plantation, which is totally out of place.
Regardless, while the film may be harrowing and difficult to sit through, it is simply brilliant all the way through, and by far the most honest depiction of slavery that I've ever seen.