The Claws of Axos (Third Doctor).
A good alien invasion story that actually feels like it is too short. It seems like there probably should have been more. In a funny twist instead of invading and taking over the planet, all the aliens want to do is eat everybody and move on.
The production design for this serial was excellent. The ship felt like an organic being, especially in the space scenes where it pulsates as thought it's breathing. The true form of the Axons is also intersting. They're grotesque enough that it makes sense that they would camouflage themselves when they deal with the humans.
My only problem with the story is the Master. Delgado's performance was excellent as usual but the character had almost nothing to do. The only purpose he serves is to help the Doctor repair the dematerialization circuit in his Tardis and then dissapear.
Four to Doomsday (Fifth Doctor).
The idea of an alien, who hopes to recreate his civilization as robots, thinking himself god is an interesting one. Unfortunately the character wasn't well written. He spends most of his time in the throne room wondering why he can't see the Doctor on his monitors and ordering around his flunkies. When he finally exits the throne room, he is immediately killed by his own poison.
Unfortunately none of the companions came across to well in this serial. Adric supports Monarch for a reason that is not well explained, Tegan tries to take the Tardis and abandon the others, and Nyssa is given nothing to do except to stun a couple of the robots and stand around.
That said, Bigon was well written and the idea behind him, Villagra, Lin Futu and Kirkutji deserved more time. Why take all these people from Earth, turn them into robots, and have them take care of the ship. Why doesn't Monarch use his own people for that?