The range of camera effects at the disposal of the Doctor Who production team in 1963/64 was incredibly limited, but The Ambush has some very effective shots (which were also quite easy to achieve).  Inlay effects are used to show the Dalek lift moving up and down and also a section of wall scorched by a Dalek gun.  Simple stuff, compared to what can be achieved today, but it works very well.

The Doctor’s capacity for self-preservation is still very much to the fore –

DOCTOR: Lets get back to the ship.
SUSAN: No, no, I must warn the Thals.
DOCTOR: Susan.
SUSAN: We can’t let them walk into a trap.
DOCTOR: The Thals are no concern of ours. We cannot jeopardise our lives getting involved in an affair which is none of our business.
BARBARA: Of course it’s our business. The Thals gave us the anti-radiation drug. Without that, we’d be dead!

The ambush scene is a little odd. Before the Thals arrive there’s a creepy scene showing the Daleks slowly backing into the alcoves. If they had stayed there and killed the Thals from the shadows this would have made sense. But instead, as Temmosus makes his impassioned speech about working together, the Daleks move out into the open. Since the Thals would have expected to meet the Daleks, why would they hide themselves?  It makes the moment a dramatic one, but that’s about all.

Also, why does Ian just stand there waiting as the Daleks move into position? He seems certain that the Daleks mean the Thals harm, so it’s baffling that he doesn’t speak until after the Daleks have opened fire.

This is very much Ian’s episode and it goes without saying that William Russell is very solid. And as the Doctor spends his time researching the history of Skaro (seemingly caring little for the modern-day plight of the Thals) it falls to Ian to try and make them understand that they may have to fight to secure their future.

ALYDON: If only I knew why the Daleks hated us. If I knew that, I, I could alter our approach to them, perhaps.
IAN: Your leader, Temmosus.
ALYDON: Yes?
IAN: Well, he appealed very sensibly to them. Any reasonable human beings would have responded to him. The Daleks didn’t. They obviously think and act and feel in an entirely different way. They just aren’t human.
GANATUS: Yes, but why destroy without any apparent thought or reason? That’s what I don’t understand.
IAN: Oh, there’s a reason. Explanation might be better. It’s stupid and ridiculous, but it’s the only one that fits.
ALYDON: What?
IAN: A dislike for the unlike.
ALYDON: I don’t follow you.
IAN: They’re afraid of you because you’re different from them. So whatever you do, it doesn’t matter.
DYONI: What would you have us do? Fight against them?
IAN: I didn’t say that. But you must teach them to respect you. Show them some strength.
DYONI: But you really believe we ought to fight.
IAN: Yes, I think it may have to come to that.
DYONI: You understand as little about us as the Daleks do!

Barbara later comments that “I don’t understand them. They’re not cowards, they don’t seem to be afraid. Can pacifism become a human instinct?” But the Doctor’s not concerned about the fate of the Daleks and the Thals and is keen to leave.  Ian, Barbara and Susan may feel more invested in the Thals’ fate, but they also agree with the Doctor that it’s time to move on.

Indeed, at the end of this fourth episode it does feel that the story has come to a conclusion. We didn’t witness the fate of the Tribe of Gum, so would there have been an expectation of the audience back in 1964 that this story would have been any different?

The Doctor’s missing fluid-link is the only reason that he decides to stay – ensuring that he’s forced to help the Thals (although as we’ll see, he’s ruthless in using them to help himself).