Compare the first scene of The Ribos Operation to that of Genesis of the Daleks. The one thing that both scenes have in common is that there is a strange, godlike being who appears out of nowhere to send The Doctor on a special mission. In Genesis, an unnamed Time Lord, standing with The Doctor in a battlefield wasteland, instructs The Doctor to destroy the Daleks or, at least avert their creation. In the original script, it was intended for this scene to be set in some peaceful, pastoral garden before David Maloney and Philip Hinchcliffe altered the scene to be set in the wasteland, as they felt the garden setting wouldn't have any impact.
Where does Ribos start out? In a peaceful, pastoral garden. It's a sign of how much has changed in the presentation and style of Doctor Who since those heady days in the programme's history when Mary Whitehouse wasn't critiquing every move the BBC made with their flagship family programme. The scene in Ribos works, though, despite how inappropriate it would have been in Genesis, mostly because of the sheer eccentricity of portraying a Guardian of the Universe as a kindly, Southern gent, sipping mint juleps in the Georgia summer sun.
The new companion, Romana, is introduced in this episode, too. The initial friction is superbly written and performed, although it's a shame that a lot of the energy in the recorded scenes had to be so obviously excised from the finished episode for timing reasons. Never before has there been such a comedic tension between the new companion and The Doctor, and it works very well here because it is soon dispensed with before the shtick gets old.
This is an episode that also sees The Doctor and Romana barely involved in the story, a story that is remarkably dialogue-heavy and features many more scenes with guest actors than the regulars, and yet it is a remarkably entertaining view. One can credit Robert Holmes for this. No writer has ever been as skilled at weaving an entertaining story around a fascinating set of characters who occupy the screen for the majority of the run time, and yet have The Doctor and the companion be so separate from the events that are occurring.