Technically I think this falls somewhere in my earliest watching of Doctor Who. In the late 90s BBC2 started showing Pertwee episodes, I missed a bunch of them, but I think I caught a few of Spearhead, and a few from this serial. However, I can't remember any of it. So it's also a nice little flagpole moment for me.
It doesn't hurt that it's rather a brilliant serial. An ancient lizard race born on Earth, went into cryogenic suspension, only to be woken up by a nuclear facility getting up and running, and them making a deal with a scientist for access to their secrets. Only they don't intend to share. Either their secrets or their planet.
Yet Doctor Who takes an almost unheard of step and keeps the 'monster' hidden for three episodes. The occasional glimpse of a hand, or a first person bit with a third of the screen tinged red (representing their third psychic eye) all the audience gets to see. It keeps the Silurians incredibly mysterious, as they should be at that part of the story. When we finally do get to see one we get Pertwee's excellent moment at this point of their introduction of “Oh Hello, are you a Silurian?” and sticking out his hand. It's an absolutely sublime moment, and one that you can't imagine any other character on television with getting away with.
Even then the producer's keep the monster in shadow for a bit longer, keeping a little of the mystery there. Well, for half an episode. Then it's all thrown out the window and those four obvious rubber suits become main characters. But this is where the genius of the Silurians comes in.
They're not a simple monster race, but actually made up of individuals. Usually the aliens in Doctor Who are just out to takeover/kill/nick our resources. Here, yes the Silurians want their planet back, but they can't decide how to do that between them. The leader is open to negotiation once he meets the Doctor and realises the Earth has been inherited by a race that followed them. Their second in command wants nothing more than to just wipe out the 'dirty apes', matching the moronic militaristic stance the humans have with the head of base security. Finally there's the realist scientist guy who can see both sides of the argument, wants to study how everything has gone, and then eventually just gets dragged along for the ride as he's not mentally strong enough to resist.
There's also the added benefit that being that they're from Earth, and were just riding out the dinosaur extinction event (maybe, the timings a little weird there) that they're not quite so in the wrong as your usual alien invasion is. They just want their home back. Unfortunately, some of them are being dicks about it.
The fact this is all going on through dodgy rubber suits is impressive, and other than that the only thing that slightly spoils them is an over reliance on their psychic abilities to just handwave a lot of what's going on.
Yet, the escalation of the problem between the two sides is entirely down to the stupidity of close minded aggressive military minds. The blame rests on two very distinct people. The head of security, and the Silurian number two, who murders their leader so he can get his way and kill off the humans, with a plan that really has no chance of working, but he believes it will because there's no way the apes are clever enough for it to fail. It's a great lesson in open mindedness, and bigotry.
In fact, the one big issue I have with The Silurians is the ending. The Doctor wants to slowly revive the Silurians and negotiate peace once more, figuring that without an army, tensions won't escalate. The Brigadier has other ideas and blows the base to kingdom come instead.
It's left ambiguous as to who ordered it. The acting by Courtney seems to suggest he's had enough and won't risk them being released again, but Liz gets a line to absolve the Brigadier of such an act. The Doctor is rightly horrified, as he hasn't yet hit a point in his life where he'll have to make such a decision, though he came pretty close today with his nuclear meltdown gambit. In other circumstances this would result in the Doctor cutting off all contact with the perpetrators and vanishing in the TARDIS. Of course that's not an option, he's exiled and we know that he hangs out with UNIT for the next three or so years, and the Brigadier remains a friend he visited often all the way through to his Tenth incarnation. It just doesn't make sense.
It also feels a little too early for this sort of fallout. We're into the second adventure of the Doctor working with UNIT, and the fourth working with the Brigadier, and they break one of his biggest rules. This should be the end of the relationship. At the end of the first season it might be more understandable why the Doctor would forgive it, but this early?
It'll be interesting to see how – or if – the show deals with this. Even if The Ambassadors of Death wasn't on my list of serials to watch, I think I'd be inserting it just to find out.