Not 'mafia' related per se, but definitely drug and gang culture related with brilliant characters 'The Wire' is a fantastic series to watch, really epic in the amount of detail it covers also. Also Breaking Bad is really good too.
I'm also tempted to rewatch the sopranos again sometime soon, it's amazing thinking back on it how brilliant the Sopranos was at its best, when the top writers were involved, it also dipped in parts when they left the writing to others but picked up again rapidly when they re involved themselves. Some really classic episodes like Pine Barrens above, ...Meadow going to check out colleges and Tony spots the guy in the witness protection program. The Big Pussy Bompenseiro death on the boat. Adriannas murder, Furio getting worried. Steve Busemi final ep, Really great tension in all and many more.