SSJAniFan explains the heart of the show. Lupin The Great (English Title) funneled through the Anime sub-culture until it made way to Adult Swim (most immediately).
This is one of the early greats, sweeping America from the 'China Towns' of San Fran, Toronto, Seattle and New York in 1975. Some have compared this show to "Scooby Doo", but the show is more sophisticated, with plenty of 'adult' content as earlier noted.
The one overlooked aspect of the show is it's English language cast, which includes the indelible Tony Oliver. Anthony or Antonio starred in some of the classic early Anime series, including the groundbreaking "Robotech". Along with his co-star on the show, Lia Sargent, Oliver never fails to appear in even the latest series, like "Last Exile".
Campy at times, but necessary in the sometimes overbearing world of Anime dramas. Maybe a live action version will be made someday, but I hope the charm of the show remains on the original cells.