I feel like the ingredients are all there in this episode, but the somehow they spend most of the episode just sitting there. We have a cast of interesting historical characters in a web of ambiguous relationships, in the setting of an ostensibly haunted house on the night in which one of them should write one of the two greatest horror novels in the English language … but the tension never really ratchets up above “medium”.
To be fair, it kicks into gear in the last third, when tension has been abandoned and it becomes about the lone cyberman. But that gear-change serves to highlight how relatively weak everything up till then has been.
I think the problem might be the music. Tension is a subtle thing, and it needs skilled steering — you need to stay in the shallows, neither running aground nor moving out into the main current. And music is the most powerful and expressive tool for this kind of navigation. When tension needs to be racheted up, music subliminally tells us that things are getting more serious; when the arc of tension needs a moment of relief, it’s music that tells us that, too. This episode felt rather as if Light Tension music from a sound library had been pasted over the episode more or less at random, undercutting the work of the actors.
Best moment for me — best by far — was Mary Shelley’s talking the half-converted cyberman down by reminding him that he had loved and been loved and had children of his own, only to find that he now held all those things in contempt and was just as determined as ever to push on with his plan. (Admittedly it would have been better still if I’d understood more clearly what his plan was.)
The worst moments were swift to follow, though: first, the Doctor’s clichéd and bankrupt moral calculus, valuing the life of Shelley over those of billions of people in the future, because of the influence of his poetry; then simply giving the lone cyberman what it wants despite the whole point of Captain Jack’s thread in Fugitive of the Judoon being that she absolutely must not give it what it wants. This last is egregious not only in that it invalidates the purpose of Jack’s being in that episode, but more — that it makes the presence of the Doctor herself in this episode absolutely irrelevant. Nothing turns out different than it would if she had simply taken a week’s holiday in Bognor instead.
So, all in all, an unsatisfying missed opportunity.