Absolutely loved this one – the first couple of episodes, on board the trapped spaceship, are wonderfully creepy, especially the first appearance of a Sensorite, floating menacingly outside the window. I also like the way it suddenly turned into a Machiavellian political drama half way through, with the power struggle between the the Elders and the City Administrator.
However, this was the earliest serial that I could sense was dragging on a little bit. They hadn’t yet figured out the optimum length for a serial – there was a lot less faffing around in years to come, once they settled on “four parts as default, six for special occasions”.
That said, I can’t find much to fault this story on. It’s an early example of The Doctor (and the audience) assuming that alien = enemy, only to find that it’s much more complicated than that. Oh, and RTD is clearly a fan of this serial too – not only are The Ood the natural successor to The Sensorites, but this story also features Susan giving a description of (the yet-to-be-named) Gallifrey that matches The 10th Doctor’s account in Gridlock almost word for word.