A very decent conclusion.
Quick thoughts before I dash off:
Okay, they didn’t blow it. In fact despite some overly wide-eyed Tennnantisms this was actually superior to part one, with lots of good doom-laden foreboding, minimal explanation, and generally effective pacing and music. Plus it dropped Comedy!Rose and replaced her with RipleyinAliens!Rose. Which was better. She got to shout like Ripley, organise the group like Ripley, crawl through ducts pursued by aliens like Ripley, and even blow something into deep space like Ripley.
I especially liked all the material surrounding the Doctor’s descent into the Pit, and particularly his sober ruminations before releasing the cable and dropping into the darkness; that scene was the heart of the episode for me. Likewise the supporting characters got some good material and were at the very least sufficiently well-developed to care about them; and also to remove my worries about their one-dimensionality.
The demon itself was a little too Balrog-esque, and also far too humanoid for a Creature From Before Time! However I liked the idea of it escaping from its prison mentally, and I was genuinely surprised when Toby was revealed to be still possessed. (So I’m gullible). The fanboy in me also appreciated the references to Daemos, Draconia and Kaleds. I know some will be annoyed about the Doctor citing Rose as a sacrifice rather than worrying about all the humans, but once again it’s clear he wasn’t discounting the others, merely focusing on Rose as his item of faith. And he did regret not saving the Oud. Tennant’s performance was variable but still one of his most subdued and consistent so far, and I did enjoy the rapid jump cutting as he tried to work things out in his inimitable (i.e. loud) fashion.
My biggest criticism is that the Tardis couldn’t possibly have fallen down the Satan Pit, which was still sealed at the time of the original collapse. (Annoying Fanwank: the Tardis’s defense system activated and it dematerialised on the way down, reappearing in the pit.) Also the Doctor hearing the rocket launch from 20 miles down was perhaps unlikely but, hey, he’s a Time Lord. And sound carries in those caves.
Overall an entertaining two-parter with plenty of the elements I enjoy in Doctor Who – a blend of horror, SF and good characterisation of the regulars. Nothing too original – almost entirely unoriginal – but very effective nonetheless. Still not a perfect score for David Tennant, but he went over the top in roughly the right places and so was largely successful.
EDIT: Oh, and next week’s episode looks rubbish. But how often have I said that and been pleasantly surprised. (Equally how often have I not said that and been sadly disillusioned.) I’m concerned by Peter Kay as a villain; although it does seem as if he’s playing a pompous buffoon, which could work if done as a character and not as “Special Guest Villain: Peter Kay”. (Simon Pegg managed it last year, after all). I’ll be away in Orkney both next Saturday and the one after so you’ll all know how it turns out well before I do.
EDIT 2: I meant to say: how appropriate that the team had a “Destination: Moon”-style cigar-shaped spacecraft which could have come straight out of 1930s SF.