I'd love to live in a house that big on my own! I live with DP and a lodger and, although I like it most of the time, I have a constantly running fantasy about living alone and rattling around in a big house. 
I agree with Moving that the BBC needs a Head of Drama Finales, or a Last Episode QA Officer, or something. This really felt like something that had slipped through the net. If it had been a play or maybe a film, it might have worked better. Plays make you use your imagination in non-linear and demanding ways and can 'get away with' more; films can create and sustain an atmosphere through action, character, images and sounds that are contained and intensified by only lasting for one sustained period of time. I think in another medium I might have enjoyed all the stuff that, as a TV drama, was just unsatisfying and obscure.
I am intrigued to see some of his films and plays now; I'd like to know if they share characteristics. The Weir is a very well-thought-of play, I think.
On another note, the dog in a bag was a bridge too far. If they needed a plot device, couldn't she have taken the kid to hospital and stolen some sedative or other drug from there? Although I do see it's interesting that someone with 'no feelings' could find love and caring for a dog where she often couldn't for people.