These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Growing the Beard: As far as the series is concerned, the first season kind of falls flat; between the single camera format and the Laugh Track, it comes off as just another standard, generic 60s-era sitcom (despite premiering in 1970). With the second season bringing us a switch to a multi camera setup with a Studio Audience, and Tony Randall and Jack Klugman feeding off the audience's spontaneity, the series began to jell and find its voice.
The movie could have starred Tony Randall and Jack Klugman.
In "The Pen Is Mightier," after hearing Felix's poem "Ode To A Skyscraper," Oscar begs the question "Who's going to read a poem about the 40th floor except a sensitive window washer??" Twenty years later, Barenaked Ladies recorded "When I Fall," a song about a sensitive window washer. (No mention of the 40th floor, though)
Ho Yay: And not just to modern eyes: Many a joke has been told about the peculiar nature of Oscar and Felix's relationship over the years. ABC was nervous about any such implications, which led Randall and Klugman to playfully film extra scenes with the Ho Yay dialed Up to Eleven, just to give the censors fits.
Informed Wrongness: In "You've Come a Long Way, Baby," Oscar is treated like a complete heel (by Felix, his girlfriend Nancy, and the background music) for wanting to call the police and report a baby that was left behind by his mother at Felix's office several hours before.
Values Dissonance: "The Pig Who Came to Dinner" featured a guest appearance by Bobby Riggs in which he played up his misogynistic public image. If similar statements had been made about blacks, for example, they would never have been tolerated, but women were apparently Acceptable Targets and Riggs' bigotry was largely played for laughs.