I think The Christmas Invasion is a pretty clever introduction for the Tenth Doctor on RTD’s part. By holding him in reserve for most of the episode we’re confronted with a world where the Doctor isn’t there to save the day - something Russell would return to with even more devastating effect in Series 4.

It’s nice seeing Rose manage things on her own and show off what she’s learned, even though it’s not enough to take the Sycorax down at the end of the day. Her acting as solo lead for most of the episode lets us catch up on her relationships with Jacky and Mickey a bit further, and shows Billie Piper’s chops as a leading actress.

Harriet Jones’ heel turn is a major sticking point for many viewers of this episode, and I agree that the way this pulls such a 180 from what we learn of her in Aliens of London/World War Three is a bit rough. Still, though I think I would have preferred at least one more Harriet appearance in between that two-parter and this episode to give us some more time to build it up, I do think it’s realistic. Showing the fallibility of our leaders is right in line with RTD’s skepticism toward the political class that we see in so many of his other episodes, and for what it’s worth, it is emotionally affecting in this case.

We could argue if the Doctor is right or not to do what he does in destroying her career, but it doesn’t feel to me as if the text is asking us to side with him on this. Coming as it does right after his “No second chances” moment with the Sycorax leader, we see that this new Doctor can be just as ruthless with his favorite species as he is with the aliens of the week. I believe this is the start of the arc that we see conclude in Waters of Mars and The End of Time, where this Doctor grapples with his tendency to play god with history.

Finally, as a Christmas episode, this story captures the vibes of the season and makes for great holiday viewing, even aside from the episode’s individual merits. I rate it quite highly.