What film, show or game that is not necessarily 'underated' didn't have the level of social impact it deserved.
What's the antithesis of Arrested Development, Firefly or The Big Lebowski? Those may never have 'found their audience' but over time seemed to recognised by everyone. What are the deep cuts that you liked but it feels like everyone has completely forgotten they even existed.
I only yesterday learned that some education instituitions in the US and Canada had limits on the number of Jewish students who could attend. The European countries who practiced this weren't so much of a surprise to me, but the fact that universities like Harvard did this was an eye opener.