I have strongly mixed feelings about it.
One problem was, I saw it at a neighbourhood type theatre and the sound was muffled in places so that I was distracted by missing some of the spoken lines. And the screen wasn't high quality so that I missed such brilliant filmed clarity as there is. I think the poor screen quality blunted some of the scenes' impact.
I have to cop to finding the movie tedious generally and at times irritatingly so. I kept glancing at my watch, not wishing the movie was over but wishing it could pick up its pace some.
Which isn't to say it isn't strongly affecting. Clearly it is.
But other than the poor screen quality, I don't know why I wasn't fully feeling it. There is for me something detached and distance-making in the film making. I couldn't get inside it emotionally though for sure individual scenes shocked and horrified me.
A few points among the many that could be made:
I didn't feel like twelve years had gone by. There was something static and staged in the movement of the story, like the movie was more a series of staged scenes that were united by subject matter but lacked being part of a dynamically moving story.
I think Ejiofor was inert in his acting. But I have a two sided reaction to it. I think in his acting and as he was directed, he and McQueen were trying to convey his sheer powerlessness. And there was something intensely anti heroic in his needing to whip Patsey and in his inability to stop Fassbender from doing it. Every internalized Hollywood instinct made me wish for some last minute save of her by Northrup, that he might turn the whip on Fassbender in some Django Unchained revenge fantasy. But of course he couldn't; and the directorial restraint in Northrup needing to cow-tow to Fassbender and do some of the whipping, however half heartedly, is shattering. So I could appreciate the quietude in Ejiofor's acting. But the suppressed rage, the internalized fury of his frustration, his longing for his family, all that kind of emotion eluded me. So I found his acting paradoxical.
Myself, I find a clue to the-for-me inert, staged quality of the movie in what is effectively a jarring set piece of liberal piety in Brad Pitt's speech. It was so heavy handedly didactic and so at odds with brutal, unsparing and effective realism of the slavery shown throughout the movie. I have to wonder what McQueen was thinking.
A final note: I noted on FB that I saw Broken Circle Breakdown. I was so moved by it that I didn't feel like carping about the odd this and that. I feel no such compunction about 12 Years.