The Reign of Terror (First Doctor).
I've always liked the Hartnell era historical serials and this one continues the tradition though The Romans
and The Aztecs
were better. Like most six part stories from the 60's, it tends to drag in the middle before picking up in the end. The animation for episodes 4 and 5 ranged from good to mediocre. Some of the character models were excellent, other were poor and the animation was stilted here and there.
I think the simpler character models in The Invasion
worked better. True, the animation could be just as stilted but it didn't take me out of the show as much.
Mawdryn Undead, Terminus and Enlightenment (Fifth Doctor).
Although known as the Black Guardian trilogy, the guardian had little to nothing to do in these three serials. That said, I enjoyed each story with Enlightenment
taking the prize as the best of the lot.
It was good to see the Brig in action again but I think he was underutilized. It was also odd to see him retired despite the fact that he appears to have been re-activated in Modern Who.
Terminus was probably the least of the three but still had a good story. The fact that Terminus caused the Big Bang is something that could have been explored more. Right now, it just feels as though it were dropped in. At least Nyssa was given a decent reason for leaving thought I wish she had stuck around.
Enlightenment actually gave Turlough something to do besides look like an idiot while failing to kill the Doctor. The Eternals are an interesting concept that I'd like to see again. Then again, I wouldn't mind seeing the White and Black Guardians again either.