The reasons why Robot would be so different from Tom Baker stories going forward is obvious in hindsight. Instead of being the first story shot for a season, it was the sixth and last story shot by the Letts/Dicks team as part of Season 11 and held back for Season 12. And it certainly feels more of a piece with that sensibility than the Hinchcliffe/Holmes team waiting in the wings.
Even within that context of a mixed heritage Robot is a bit of an odd duck. Shot entirely on tape, it necessarily lacks the visual polish that so benefited Spearhead From Space and the humor, while interesting, is not of a piece with either what came before or what would be coming. Tom Baker is up for all of it, so it gave the audience a chance to see his range, but he seems especially googly-eyed here as well as a bit manic. This is why Robot is atypical, but still elicits a smile upon re-watching.
Did we mention the schizoid Robot which grows (and glows via the miracle of rudimentary CSO) to giant-size? All part of the charm of course.
