Saw it earlier, and enjoyed it enough. A couple of things bugged me, like the weird plot device of Katie having given up Hunter, only to get another child and go get the original one back. Hopefully that gets explained in 5.
I loved the Kinect particles and wish they'd used that more. Very clever way of building tension, somewhat like the oscillating camera in 3. There was some weird stuff like questions as to why people were still filming at points towards the end, but that can be applied to many films in this genre.
Also, what was with that end credits scene? Was that a hint to what we'll be seeing in the fifth movie?