If there's a fault it's that once the darkness begins to overwhelm it, at about the halfway point, it begins to follow a more standard path to a showdown conclusion. As others have commented, there's enough inventiveness with the found footage premise that it doesn't feel intrusive after a certain point (as the camera is functioning more like it would in a standard movie) although I'm still not a fan of the sub-genre.
The performances of the main trio are top notch. Not having seen the Friday Night Lights TV series, I hadn't realised The Wire's Michael B Jordan had grown up to be such a charismatic presence (but it is 10 years since he played Wallace!) And Dane DeHaan does indeed have the air of a young DiCaprio about him. I can only put the SFX in this looking so good (in comparison to a film with 3 or 4 times the budget) down to Trank's eye, and understanding what will work and where. There are moments, such as the fate of a spider, where it's abundantly clear that this guy is employing effects to tell a story not dictate it.