I really liked how the Doctor was so helpless in that episode, I thought it added to the tense-ness, since he was as clueless about what was going on as we were. I'll say it, that episode was pure frightening!
It felt so different to the other episodes too.. as you said N.A.G.A.C.E, he didn't save the day or anything, the 'monster' lives on and it's all left unresolved.. it was more like he escaped than he emerged victorious.
Great villian (kudos to the actress, the look in her eyes was so unnerving.. fine performance), the echoing of the voices in the background while they talked was really ominous, her presence was always there keeping up the tension. I kinda thought it a breath of fresh air, the feeling of claustrophobia as opposed to the usual grand landscapes and settings, the Doctors vulnerability as opposed to always being in control surrounded by people who respect and listen to him.. nice one Russell.
Rose on the monitor was hardly subtle, was she?