I remember this as the first Doctor Who episode I ever saw and being disappointed that Jon Pertwee (whose face I knew from magazines and comics) had just left the series. If I had known how important Tom Baker would turn out to be, I would have looked at this episode differently. I can do so now.
Terrance Dicks mentions in the commentary on the DVD that he wanted the new doctor to be a bit more crazy. If he appeared to be too wild, they could tone him down in the next few episode/serials. Upon watching this episode again after all these years, Dicks admits he might have gone a bit too far. After the initial confusion of the regeneration, Baker seems to channel the three Marx Brothers. (It is impossible to channel the fourth brother Zeppo, the bland Apart from the fact that Baker bears a strange resemblance to Harpo Marx, there is a short scene where he dresses as a Pierrot and sulks exactly like Harpo. Making Harry Sullivan join him in a childish game of rope-skipping is pure Chico Marx, whereas his argument about being 'the' doctor could have come from the mouth of Groucho Marx.
All of this is enjoyable, but it can't hide that the rest of the episode is bit flat. And having just learned that Ian Marter, who joins the cast as Harry Sullivan, died quite young and had been poorly before this episode, I found the weird irony of the doctor and Harry questioning each other's health rather unsettling.
(PS: I know. There was a fifth Marx Brother, Gummo, but he never appeared in the