He steps out of the shadow in which he is hiding, and grating in his best impression of a Dalek voice, "I am your ser-vant." Robert James is great throughout, but his final moments are superb.
It's especially chilling because he is, at this point, completely sincere.
There are other deliciously creepy bits--the assembly line of the newly fashioned Daleks is beautifully animated, and flows much more naturally the human movements (my main complaint about the animation is that walking looks all too often like sideways hopping), the massacre of both the rebels and the guards by the Daleks--while the usurping Lieutenant Governor Bragan thinks his plans are working, humanity within the colony's capital is being efficiently wiped out.
There are moments that are touching--Valmar's sincere grieving for his colleague and fellow rebel Janley. In the wasteland her errors have indirectly caused, he can't leave her body, and murmurs, "She wasn't as bad as you think" to the Doctor. (Richard Kane infuses a touch of unexpressed passion in his dealings with Pamela Ann Davey's all-business Janley, and it adds to the poignancy of the moment.)
This is the first Dalek story to raise the threat level the pepper pots pose to the level they now do; the Doctor notes that all is not well with the colony, and then adds darkly, "Add to that one Dalek." Ben replies, "Oh, blimey, you don't half make mountains, don't you? One Dalek?"
The Doctor's answer will be echoed throughout the history of the program, most notably by Christopher Eccleston in 2005: "Yes! All that is needed to wipe out this entire colony."
So too will the "I am your servant" ploy reappear:
All this, and the first circle chanting "Exterminate!" "Exterminate" over and over again. We're setting some show standards here in this episodes, codifying tropes that will go on for half a century. And such is the cleverness of David Whitaker's script that the characters who are caught up in it all--the double-dealing Bragen, the honorable Hensell, the cold-blooded Janley, the enigmatic, flippant Quinn, and the tragically self-confident Lesterson--are each distinct, important characters. They're interesting in their own right. Even Janley's death, telegraphed as it was, counted for me, and Hensell--Doctor Who's early version of Ned Stark--dies rather than dishonor himself. And you believe it.
In a way, these last three episodes of political intrigue, the Daleks being cunning instead of only blazing away, and the Doctor's brilliant (or lucky; the episode seems genuinely ambiguous) is Doctor Who on good form, but not spectacular. But think about it, for a second, what has been accomplished.
A new Doctor has been inaugurated, in a painful process that acknowledges the pain of the loss of Hartnell, and the need to regain the audience's trust;
The Daleks are back, an existential threat in essentially the manner they will hold for the rest off the classic series, and, frankly, through the revival The Daleks remain the parable of nuclear war they always were, but now have a motive beyond their old enmity with the Thals:
POLLY: You've all underestimated these Daleks.It's been intimated before, but Polly's articulation of it rings down the decades;
KEBBLE: Better brains than us, I suppose.
POLLY: I only know what the Doctor has told me. He says they're capable of exterminating whole nations.
VALMAR: Perhaps, but what would they want to kill us for, after we've taken over. We're friendly with the Daleks.
POLLY: But don't you see? Human beings can't be friends with Daleks. They don't have friends.
VALMAR: I don't see why not.
POLLY: It's a kind of hatred for anything unlike themselves. They think they're superior.
VALMAR: The girl's got something.
And a story of human vulnerability has been told--how we are capable of unleashing forces that seem benign but escape our control.
Just the story we need at this time, really.