I would actually say that movie lacks soul.
Almost famous has soul, Forrest Gump has soul, The Accused has soul. Twelve Years a Slave, after the initial shock and horror at he beginning where he was woken up and beaten, the movie felt very flat. Every 15 min or so he or another character will get more physical abuse but that alone doesn't make a great movie, it makes a decent documentary. Perhaps the lack of justice is what is the downer in this movie, I wanted all those people who treated him badly to get the justice they deserved but that never happened.
Also, I really struggled with some of the very repetitive scene where the camera just sits there, 20 seconds go by, nothing happens, it's either his face or the swamp or some tree. I understand why that was used but it happened too many times.
I actually thought Django Unchained portrait slavery just as well (in a bad light) yet a better movie. I guess 12 years when you finished watching it, you haven't come out with anything you've not seen before, it doesn't show anything you didn't expect to happen. It is exactly what you think happens, happened. But I can't say predictable is a bad trait, Titanic is predictable but it's also a better movie, 12 years a slave just felt flat. The moment he was captured I was waiting how he is going to get away, that took another hour and a half which was too long.