The very first scene of The Armageddon Factor, that of an overacted soap opera on Atrian TV, would seem to be made entirely tongue-in-cheek, complete with the horrible fringing that is so prevalent in 1970s CSO work. But then, given that so much legitimate CSO work on Doctor Who looks like that, anyway, I'm not so sure how where the line is drawn between knowing pastiche and technical limitations.
I don't mean to pick on small time actors in even smaller parts, but poor John Cannon, who plays the guard entrusted with the task of escorting Princess Astra around before he's shot by his own superior, the Marshal, is just not an actor. He mumbles his lines with zero regard for intensity or passion, and I would love to hear what (an unheard) Marshal was saying to him on the other end of their conversation later in the episode, as Cannon leaves almost no time in between his lines to allow anyone to speak. You can almost tell that director Michael Hayes realized Cannon's limitations, as during a conversation between Astra and the guard, Hayes decides to keep the camera on Astra during the entire scene.
On the other side of the acting scale, though, is the incomparable John Woodvine, who surely must have one of the best voices of any actor working in British TV. Woodvine is note perfect as the Marshal, blustery when he has to be, but also intense during his scenes where he's "meditating". My favourite little scene of his in this episode is his gleeful reaction to the supposed destruction of the TARDIS: "We got it! Destroyed it! Smashed it! Vaporized it! Beautiful!". This is a man in love with war and all that comes with it.
And remember when I said that Mary Tamm looked her absolute best in the red dress in The Stones of Blood? I was entirely wrong. Tamm is utterly divine in her white dress and boots in this story. With respect to all those who came before and after her, no companion has ever been able to combine posh class and intelligence with pin-up girl looks like Tamm.