Shatner's first Columbo is interesting because Walter Koenig pops up in a small role.
What's odd about it is it doesn't feel like an intentional gag. The two aren't on screen together, there's no cutesy references and Walter's part is all of three lines. It feels for all the world as if it's just that his career was just in a place where thankless bit parts were all he could get and cropping up in the same show as Shatner was just a coincidence.
Shatner's second Columbo is interesting because of the deeply silly moustache he's sprouting. Which grows and shrinks across the film (Falk's hair is noticeably dyed much darker in one scene as well, all of which makes it feel like they did some shooting much later than the bulk of production).
There's an episode of Lois and Clark where Jonathan Frakes (along with his wife) is introduced to the scenery and given a knife and fork before being told to chow on down.