One of the few horror movies that I ended up watching in the past few years. It is mostly like any other horror movie where a family moves into a new home which unbeknown to them is haunted. As time passes the haunting becomes obvious and they decide to take help.
One very ironic thing that I found was that in the movie Ed Warren hesitates a bit before performing an exorcism; because he is not authorized to do it. He needs to provide proper proof that a given person is possessed and only then will the Vatican send in an authorized exorcist to expel the demon.
Otherwise the movie takes itself seriously enough to be scary to most people and you can enjoy it if you let your guard down a bit.