Come on people, Godfather 2 is the ultimate gangster story.
Firstly the whole concept of father and son dynasty, and how their stories interweave.
The movie has it all from the moral dilemmas of Michael in his flirtations with legitimacy are compelling since a streaming amount of loose ends and bottomed-out business deals never tie up neatly for the execution of the family's illegal activities. Instead, an intriguing federal investigation into the family hinders the process. The Shakespearean suicide of the disgraced Mob informer, the execution of a family rival and the shocking execution of Fredo end the film in a great collage reminiscent of the first film's spectacular conclusion.
I still beleive that the original Godfather is better, Zed. However, all the things you said about part II are true.
Part I was brilliant in it's own terms. Here we have a war hero who wants the normal life. Michael understands what his father represents, and wants nothing to do with it.
Then the attempted assassination of Vito draws Michael into the world, and he eventually runs the show himself.