Lots of "boo!" moments, but very well done. Scared me silly!

Rating: 8/10 (7 May 2013)

EDITED: Feb. 27, after 2nd watch.
I've just finished watching Sinister, and I must confess that my heart is still pounding. I hate to say it, but it made me jump in my seat a few times. Why do I hate to say it? Because as a devout and pretty experienced Horror fan, I really find it hard to respect films that use "cheats" (i.e slow shooting with very dark lighting, suddenly a frightening shot with a blast of loud bass music) that appeal more to a viewer's physiology than their logic and fear. Still, if you're gonna use that "cheat", then this is definitely the way to do so! Sometimes it's real fun being scared like that.
I didn't find the screenplay and story to be all that original, as we've seen many films using very similar backgrounds, but I did like it. Gruesome murders, missing children, found footage as part of the plot (rather than the entire film being a "mockumentary"), and one Ethan Hawk trying to get to the bottom of all while fighting to save his career and keep his family and marriage from paying the price. Pretty decent, yet pretty generic.
Sinister uses elements from different sub-genres and adds them up together to give the viewer a very healthy scare. I especially liked the fact that the audience can't really know what type of Horror film this is (Ghosts? Slasher/Murderer? Occult/Supernatural? All of the above?) until around the middle, and that unlike in other films - in this case the plot synopsis here doesn't spoil it. The acting was also good, though mainly by the rest of the cast (for instance Michael Hall D'Addario and Clare Foley as the two children, or Fred Dalton Thompson and James Ransone as the Sheriff and Deputy), I don't really appreciate Ethan Hawk's obvious overacting in this one (though I guess his acting is like pineapple as a pizza topping, you either like it or you don't).
As for the ending, I always enjoy Horror more when a clever plot twist is applied, enhancing the feeling of suspense and the using the element of surprise to increase the overall sensation of fear (very much like psycho-thriller films). In Sinister, the ending doesn't involve such a twist per se, but it definitely binds together many pieces of information and succeeds in being unpredictable and horrifying (even when watching for the 2nd time!)
One of the best features of this film is the original soundtrack, which is dark and eerie and definitely takes the overall feeling of discomfort to a new level. This is especially noticed when the protagonist watches the old silent films.
Like I've said, if you're going to appeal to the audience's physiology and jump from behind the closet shouting "boo!", do it right, and Sinister definitely does it right! Very very few Horror films in this day and age don't use any "cheats" at all, and when done well enough - the "boo!" thing isn't really that much of a cheat. I've really enjoyed watching this film, and would recommend it to anyone who fancies themselves a tough viewer. Sit at home alone, turn off the lights, and watch this. It was 8:30 a.m when I first watched it, and it still scared me silly.