"Everyone knows" that the four-part story known as An Unearthly Child is really two stories: a one-parter and a three-parter. Probably unsurprisingly, I disagree. There's a certain obvious truth to the statement, but I think they're less mismatched than people say. There's a change of setting from 1963 AD to 100,000 BC, but the Tribe of Gum extends and counterpoints the first episode's themes. In 1963, two humans stumble across the products of a civilisation so far in advance of their own that they can barely even comprehend it. They fight and go into denial, while the Doctor and Susan ignore them or treat them like children. The Doctor even explicitly likens them to primitives seeing their first steam engine.
Then back in the Stone Age, they find a world as far behind Ian and Barbara's developmental level as they were behind the Doctor and Susan. For these cavemen, fire is a technological miracle and social sciences aren't even in their infancy. "How can we explain this? She doesn't understand kindness, friendship." And then the Doctor: "These people have logic and reason, have they? Can't you see their minds change as rapidly as night and day?" They're staggeringly primitive, but they're still dangerous. You underestimate them at your peril.
The Cave of Skulls is arguably the first episode of a three-part historical (which might explain its slowness) but it's also very much part two of An Unearthly Child. It continues the story of the Doctor, Susan, Barbara and Ian, picking up where the first episode left off and extending its themes, arguments and character development.
The first episode is obviously fantastic, though a mere shadow of what it should have been. Having at last seen the pilot episode, I suspect I'll never watch the broadcast version again. From now on it's Scary Hartnell for me. Compared with that the remaining three-parter has a reputation for being a bit boring, which I can understand despite not finding entirely fair. There's a lot of good here. I like the aesthetic, for instance. These aren't glamorous "Raquel Welch in 1,000,000 Years BC" cavemen, but thoroughgoing savages that haven't been prettified for television in the slightest. It's uncompromising. There's a delicious brutality to part four's big fight, for instance. Any other story would have had the Doctor or one of his companions jumping in to save Kal's life when Za raises that rock. We've been programmed to expect it. We're waiting for it, but we wait in vain. Squish.
Unfortunately the problem is the performances. In comparison, think back to Carl Forgione as Nimrod in Ghost Light, who mostly lets the make-up sell him as a caveman and just gets on with playing the character and the situation. Admittedly the Tribe of Gum couldn't have gone that far, but visually they're so convincing that I think they could have afforded to pull back a little. Kal in particular needed to act more. He's the drag factor in episode two's lengthy confrontational scene, which is the only genuinely boring bit in the whole serial. It should have been compelling, but it drags. Derek Newark is putting in the effort as Za, but Jeremy Young's Kal is just grunting out his lines. Visually he's great, with that menacing face, but he's clearly the worst thing in the story and things improve considerably once he's dead. Until then it's basically Doctor Who's first example of Two Alien Factions and we know how badly they tend to turn out.
There are some startling accents ("Oi was a great leaderrrr of many men"), although this makes sense since this patchwork community is sheltering the last survivors of other now-dead tribes. However it's still disconcerting to get this huge range of speech, from the aforementioned Farmer Palmer or Kal's barely human grunting to Za's near-eloquence. It's appropriate for Za to be the articulate one, though. He thinks. He has ideas about what a leader should be and even if everything isn't clear in his head, at least you know he's making an effort to work it out. Interestingly though, in their own ways both Kal and Za are correct. Za's attempts at firemaking are indeed risible, about which he's a bit too fatalistic. If at first you don't succeed, plod on moronically with what you've already proved is ineffective. However on the other hand Kal would indeed be a terrible leader. At least Za has thought processes.
Mind you, I admire Kal's way of getting out of a pinch in part four. "Yes, I killed the old woman." You can't beat honesty.
The TARDIS crew are all fantastic, obviously. Note that Ian takes the bull-headed sceptic role that could have made him look like an idiot, but William Russell avoids that trap. He seems practical, not stupid. Once he's seen prehistoric Earth with his own eyes, he accepts the evidence and quietly adjusts to his changed situation. Barbara is the group's heart. "Your flat must be littered with stray cats and dogs." "These are human beings, Ian." Hartnell of course is a god, especially if you watched the pilot episode, although I was surprised by how understated is the famous moment where he's about to murder Za. I particularly love his big scene in part four, manipulating the tribe and basically condemning Kal to death. "I have never seen a better knife." "This knife shows what it has done." You get him, you old bastard! It makes the character far more interesting that in his early days the Doctor wasn't a straightforward hero but a selfish old goat willing to do just about anything to ensure his own safety.
He's obviously still unfamiliar with the TARDIS. He's unusually cautious, taking his Geiger counter outside even after Susan's checked the radiation levels. It's also startling to see how disturbed he is by the failure of the chameleon circuit. Oh, and that's a fantastic final cliffhanger. The TARDIS lands on some strange world, with a scanner image that's freakier than anything in both Cushing movies put together. Our heroes talk about going out to investigate this place from which any sane person would run in horror, then the radiation meter creeps up into the danger zone and we see the next episode caption: "The Dead Planet". I shivered.
As an aside, this story makes a perfect companion piece with Survival, together bookending the classic series. Both stories put the Doctor with another Time Lord with whom he has a long-standing relationship and some ordinary humans in two settings: (a) contemporary London, portrayed with a realistic mundanity that's almost without parallel throughout the rest of the series, and (b) a Stone Age world with nothing to offer but fighting for survival. If you really wanted to stretch the comparison, you could glue the TVM to the end of Survival and turn it into a Stone Age three-parter and a mostly (but not entirely) unrelated one-off pilot set on modern Earth in which the Doctor picks up a couple of humans but has as his only travelling companion that aforementioned Time Lord.
This story is fascinating. Its reputation for boredom is actually the fault of episode two and specifically one long-winded scene. Once you're past that, you're flying. There are some dodgy 1960s production values if you're feeling uncharitable, but personally I thought the visuals were surprisingly effective. The cavemen are almost too convincing, the TARDIS hardly ever looked better and we even get to see out through the doors! That's something we rarely got. Between Hartnell and Eccleston I can only think offhand of Pyramids of Mars. Returning to An Unearthly Child, the only silly-looking bit is the regulars running on the spot in part four. Otherwise I like the way this looks. In particular there's something primal about skulls and fire. The script has interesting themes, its TARDIS crew are vividly realised and the whole thing has electricity. It's lightning in a bottle, captured at a time when Doctor Who's formulae hadn't yet been invented. One of the best pilots I've ever seen, for anything.