This is the first appearance of the Daleks since their emperor and city were seemingly destroyed at the end of Evil of the Daleks. The thing with time travel is you can bring villains or anyone else back from the dead.
Actually, this story uses time travel in a way that hasn’t previously been done on Doctor Who. Not because it brings the Daleks back (these ones would be from an earlier time) but because it sets up a future history of world wars and disaster, caused by an event in the past, which is caused by the actions of someone from the future trying to stop the event but actually causing it in the first place. A causality loop, or as the Doctor calls it, a paradox.
This also neatly sidesteps the continuity issue with the first Dalek invasion, which by my recollection, should have occurred a couple of decades prior to the future events depicted here. If the timeline was (temporarily?) altered so that mankind nearly wiped itself out instead, the original Dalek invasion would not have happened, and instead we learn that they took control of Earth at a later date, more passively, controlling its leaders and building its workforce from the survivors. This would also mean that Susan would not have stayed behind. She wasn’t mentioned; in fact the original Dalek invasion is only referenced in passing, but it got me thinking and I enjoyed it.
The Doctor is, of course, able to travel back to the past and stop the explosion that would kill the world peace delegates and plunge the world into world war three… and in doing so, allows humanity to escape its fate. A lot of sci-fi shows and movies from this era played with the idea of atomic wars in the near future, so it was nice for Doctor Who to end this story on a more optimistic note.
Tightly plotted into four parts, this was enjoyable, thought-provoking and clever. One slight disappointment was that the Doctor’s time experiment with the Tardis control panel at the very start (they see future versions of themselves enter the room) is not followed up on. That would have been fun to see them walk in on their past selves, completing the loop, but it didn’t happen. Never mind.
It was good to see the Daleks back, in colour this time. With no sign of the Master, and the Doctor still stuck on Earth, we need more stories like this. Big ideas, played out on a small scale. This worked for me.