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.
That show had great scripts, great acting, and great visuals. I can't think of one area where the show had a serious deficiency. It was the quality of Game of Thrones before Game of Thrones. It just never caught on. I give it a rewatch once every few years.
As great as it is, you could tell they had to cramp two season's worth of story into the second season so that it felt very rushed and important side characters died off screen. And then of course the sets burned down ironically, making any continuation impossible.