Everyone I knew who had seen this movie said it was awful.. but then I watched it and actually liked it BETTER than the original movie. Not everyone thinks this movie is crap! I am a great fan of haunting-related horror movies, my favorites being the Exorcist, Blair Witch project, Ju-on, the Eye, the Ring (#1, #2 in my opinion was ridiculous), and other such flicks.
It was well made, great graphics, great atmosphere, great emotional tangibility... I really enjoyed how they portrayed the evil in this movie. It's a clean looking movie, aesthetically pleasing, and just plain well done in post-production. The acting was good, believable, and I thought it was more organic than the original. Great direction.
I was a little disappointed that they didn't have the creepy "Get Out" scene at the beginning of the book (in the movie) with the priest.. There are a few other scenes that could/should have made it into the new film, but I think it's good that they went a "different" route to distinguish the film from the original.
Overall, I say that you read the book first. It gives you insight into the matter, and helps you form your own opinion of the infamous haunting.
Like original Ju-On and the Grudge, the original Ringu and the Ring, the original Amityville horror movie and the New Amityville movie kind of "complete" one another. They explain things that the other doesn't, they go "places" that the other doesn't.