I consider Event Horizon and The Ring to be two of the scariest movies I've ever seen. I never saw The Strangers but the trailer is scary enough to convince me
http://www.youtube.com/watch?v=nCU0k_jbCUo
Yes I consider Cabin In The Woods to be a great horror movie and I'll tell you why. The satirical / parody aspect of it is so subtle that mostly intelligent people will get it or those who peruse the horror section a lot. A great example is the "Deadites" on the dry erase board with the other monsters. This is a blatant reference to the Evil Dead movies. The different quips and events that make it a bit of a parody at times are really no different than some of the one liners in The Expendable movies that the actors deliver as a way of paying homage to their action movie past. Its not there to break the continuity and reality of the movie; its more to tip their hat to great actors and movies of the past. Just my interpretation.