Spearhead From Space is an enjoyable enough romp, but that's about it. It's not really a gritty drama unlike Terror of the Autons which goes out of it's way to shock you. Spearhead is also more light hearted and comical during it's first episodes, this is due in part to it being the first story of a new Doctor. So naturally some of the scenes were played for laughs, not a wise decision to do something like that when you're trying to establish a new Doctor. And Pertwee's performance is also a bit too comical in this story.
There's a complete contrast with Terror of the Autons, which is so much more serious and more dynamic than it's predecessor. If anything marks down Terror it's some of it's visual effects. Some of the interior CSO shots of the factory and Rex's Mother's house do jar quite badly. Particularly now that the Restoration Team have got the picture so pinsharp, you can see just how in it's infancy the CSO effects were.
However despite the budget, Terror of the Autons is a good strong story. It is notable for two series debuts, the late Roger Delgado excels in his role of the Master, a part he was born to play. He also plays the part magnificently, when he pushes the technician off the ladder from the Satellite structure it is a very chilling moment. Delgado imbues the story with a sense of twisted evil and rivalry against our hero, the Third Doctor.
The other debut is of course Katy Manning as Jo Grant, a rather ditzy character who is forever getting herself into scrapes. She and series star Jon Pertwee would later develop a very good on-screen charisma with each other as the Third Doctor and his companion Jo Grant.
Terror is renowned for it's scenes of apparent everyday items coming alive and trying to kill you. A premise which perhaps was taken too far judging by the reactions to the story after it was first broadcast. Certainly it is a scary story but I certainly don't think they went too far. If anything this adventure is a one off, and all for the better. There hasn't been a story since which has used similar ideas within it's narrative structure. It's certainly a better story than Spearhead From Space, and although many would say that the Master's change of mind at the end of the story felt a bit rushed, the story does hold up very well.
It's one of my favourites and all Doctor Who fans should have a copy of the Mannequin Mania boxset in their collection.