La posesión de Mary

It's actually not so much the ability of the actors to act (I don't think anybody will see Gary Oldman and doubt he can act), but it is the script and the horror movie cliches/tropes that will likely get you quite upset. To say the least. And you also have other people in here (Emily Mortimer), who are way above anything in depth, that the movie can offer them.

Having said all that and all the things that are predictable, the movie can still be enjoyable to a certain degree/level. You have to be a fan and not mind the flaws that are littered throughout the running time.