First, some technical points. The audio mix seems all wrong, the dialog is barely audible in comparison to the rest of the sound track. I turned it right up just to hear them speaking but then the sound effects and music were way too loud. In the end I had to use subtitles, although I could hear everything else just fine, but not the dialog. And then we have the picture quality. For me it was no better than DVD. If you buy Blu Ray for the better visual experience you might as well not bother, save yourself some money and get the DVD instead.
Now, about the movie. It has a lot going for it. There is genuine tension and creepiness, and some good almost "noir" scenes throughout the setup. A simple knock at the door manages to hold more fright than your average horror scene, and this subtlety is what makes The Strangers work so well. The simple, subtle things like a masked person drifting into shot and then out again, unseen, unannounced.
The acting is good, despite other reviews, I liked it and was convinced. However, the characters are somewhat stupid in their lack of ingenuity. They are under attack in a home full of potential blunt weapons but never think to simply pick up a fire poker or a chair leg and whack the bad guy with it!
There is a strong mystery element to this film, ie. who are the strangers, and why are they attacking these innocent people? It is critical for any strong mystery to be resolved, or at least the solution hinted at, but in The Strangers we are left none the wiser. This makes for a dissatisfying experience, although the ride was gripping up until the point where you realize no answers will come. One could argue the unresolved aspect is the whole point, however I judge it to be sheer laziness in the writing.
Good film, poor ending, dodgy disc quality.