Though I think The Exorcist is matchless – remember when The Blair Witch Project * was considered a 'challenge'? – I was amazed at how good and scary this was. It's a kitchen sick of just about every hoary horror trope you could think of, yet it works beautifully. Expertly paced, determinedly restrained, sparse on CGI, ruthless towards the audience. As effective a spookfest as I've seen in years.
*The Blair Witch Project is an interesting, occasionally chilling endeavour, ground-breaking, the progenitor of the found-footage sub-genre.