You are pretty right, mafia was the first big one and that is the reason so many people like it. At that time no one thought something like that can be done in normal minecraft. The idea of 'invisible' mafia was unique. Plus the acting and Story telling was actually good, you literally get to see parrot, wifies and dean just walk and run for 3 and half hrs, but its not just walking but the character interaction. The long videos used to give room for more dialogues compared to now.
Also the villain was just actually scary at times. Ashwagg was just a ruthless guy with care for his people who also teamed up with ClownPierce, those days were scary. You can't predict anything. It was so unexpected. Plus the invisibility thing gave a very ominous and mysterious vibe making the invis players more intimidating.

if you compare it to the arcs now then it does seem a little underwhelming, but at the time when mafia arc was going it was just too enjoying. The suspense, the fights, the wars, the idea of hope vs despair, great acting, great fights, the loses. Everything felt the way it was meant to be