I think you've got one thing exactly  The Sopranos works so well precisely because it is understated, because it is the opposite of the operatic Godfather . Together, The Godfather and The Sopranos make up some kind of whole, but here's the fundamental difference between  Every mobster I've ever met imagines himself a player in The Godfather . I interviewed Sammy Gravano a few weeks ago and he said as much; The Godfather invested the lives of mobsters, who are in fact seedy and boring characters, with honor and drama.
The Sopranos is not understated at all, and is more operatic than The Godfather.