It's a slow-bulding story, with a great cast who unfortunately doesn't get a lot of moments to shine (although I think many will find Lucy Fry a nice surprise like I did!). The suspense is well done, and I did find the movie satisfactory overall. I mean, it's not amazing, it didn't make me jump, but I was entertained, and I got into the characters too. Regarding other comment on this page, I think it's unfair to compare it to Poltergeist. There are many takes on poltergeist/haunted house stories, and this is just another one. The mythology did feel a bit weak, but the story still ran smoothly despite that. Surely, the final 15min would have been better had there been more background on the Anasazi, but really, not too big of a deal once you're hooked.
If I had to mention a real problem with it, is that it's part of that trend which tends to associate children within the specter with abnormal/evil behavior. I get it that taking a "strange child" as a catalyst is great for effect, but it's a disservice to all people trying hard to bring clarity on the issue, you know? It's good for story telling and all, but a bit disrespectful, in my opinion.