"Planet of Evil" is entirely studio bound with no outdoor location shooting. All of the sets were made for the episode and the jungle planet is more real of a place then all of those gravel pits put together. It breathes with glorious light and color effects, uses what look like pottery or electrical fixtures as space plants, and has knee deep water for the actors to splash around in while evading the Id monster imported from "Forbidden Planet". With all of the effects done with in-camera overlays and weather channel type matting the SFX on display the episode may have "aged" but so have I.
Some remark that the Morrestran ship is a let-down after the jungle set and I counter that anything would have been, and the clunky right angled minimalism of the ship continues to suit my needs as a viewer just as well as the shoulder pad v-necked space suits worn by the crew. They have cool names (Ponti, De Haan, Morelli), have cool guns that make a cool sound and several are sent heroically to their deaths in the proudest tradition of the Red Shirts of "Star Trek". They are there to be wasted onscreen to absolutely petrify the 7 - 12 year olds in the audience just itching to be scared stiff. That's why we tuned in every night. Golden stuff.
Then there's the Salamar issue. As portrayed by Sheakspearan trained actor Prentis Hancock, mission commander Salamar is the working definition of an insufferable histrionic jerk ... Or is he? I prefer a different reading of the performance, which I consider perfect for the subject matter: Salamar is insane, living mentally in an alternate inner reality where his behavior is considered normal. Because he not only holds rank but has a service record of getting things done his shipmates tolerate it and act like he is just as mellow as De Haan after a few pints in the cargo hold. Because Salamar is crazy but has never gone over the line of dysfunctionality to force a subordinate to take action Until now.
Or whatever: You watch this one for the jungle set, and an interesting "Pre-Hype" performance by Tom Baker before he had become a cultural icon. He was still working on developing whom the Doctor was, and quite frankly if he'd stayed with his rather somber persona the series might have evolved a bit further. But alas, K-9 ...