Technically a streaming series rather than a TV series, but the second campaign of Critical Role (Mighty Nein). I started watching the series after seeing how popular Critical Role was online and that Mighty Nein was recommended for CR beginners, but I really didn't get it at first; it seemed so boring and slow. Still I stuck with it (listening to it in the background while I did other stuff), and I remember there were two specific moments where I finally understood its popularity:
spoilerepisode 7 "Hush" when Nott kills the manticore baby (which was my first "holy shit they did what" moment), and episode 12 "Midnight Espionage" during the hospital heist (I could not stop laughing at the debacle and completely lost it at Nott's negative charisma roll).
In other words, thanks Sam Riegel for making me a fan!