The Edge of Destruction is like the Platonic ideal of a one-off Doctor Who story. It's spooky, well paced, and tense. I enjoy how we get to see the characters in such an unfamiliar environment (because even an alien planet can be rationalised, but something in your mind onboard a time travelling spaceship is much harder to brush off). We also get to see the writers understand what will be the appeal of the TARDIS, it's not just a spaceship, she's a plot point and arguably character in her own right