One of the most underrated shows (if not the most) of all time, though not for the reasons you might think. Everyone knows the words "Star Trek" and has probably heard several references at least, so it's not underrated in that sense. However, Star Trek (The Original Series), dealt with so many severe, hard-hitting and/or real issues in the turbulent times of the 1960's that are still incredibly prevalent today. Racism, treatment of those suffering from mental health disorders, as well as gladly pointing out the flaws of the human race (among others) in a time that was so rigid due to the Cold War. For these reasons, the show certainly did NOT get lauded for its forward-thinking concepts as it deserved, (in fact, during its run time, it was panned by many officials and political figures) and now it is seen merely as a "nerdy, Sci Fi" show.
If you didn't realise, this show is amazing and you should all watch it.