Your frustration with the darkness was part of the point. Shayamalan got to you, as he intended to do. The darkness is frustrating and disorienting, much like his camera's tendency to linger on something, ANYTHING other than what you desperately want to see!
I thought it was a very well-made movie.
I know, but a movie has to be very good to hold on to me in spite of frustrating me like that. This one did.
I also didn't miss the symbolism of the last scenes being brightly lit. :=)