I've seen it. Personally I LOVED it - best horror film in years (will join the ranks alongside It Comes at Night, It Follows and The Witch for me). Most of the crowd around me? Not so much.
For the first third, people seemed to get pretty bored quickly. I'll admit it is a slow burn drama for the first section, something that I loved, but I could sense others getting restless (crinkling food wrappers, phone lights, whispering). The film really picked up in the final third, and it seemed people were mostly into it. I think the last part of the film is what people thought the whole movie was going to be. The first part is what makes the last parts so great, but I don't think general audiences either A), anticipated the pace being slow for most of the movie; or B), knew that this would be more of a physiological drama first and supernatural horror second.
My friend went to a showing today and he said that two couples left the cinema; one at the half way point, and one about 20mins before the credits (the last couple seemed disgusted by what they saw). Nobody left in my showing, and I think most were pulled in by the end, but I can not see this getting anything more than a B- on CS.