There's no difference between The Godfather and NWA's music. N.W.A.'s music is telling violent stories, stories of power, stories of an outlaw life, the same thing that The Godfather and Scarface do. Dre had great, original beats for N.W.A. (And Tupac later on) and Ice Cube had (and still has) great flow and witty word play. It's good hip-hop with violent themes, and at the time it was very original.
50, on the other hand, comes off, to me at least, as a poor imitation of that original music. His flow is horrid and his lyrical skill (ignoring content) leaves much to be desired. He doesn't tell stories, he spits lines.
You're right, it is now Gangsta gangsta gangsta. But the problem isn't that there's gangsta music, it's that there's nothing but gangsta music. Some is entertaining, but now it's to the point where it's repetitive and predictable. When N.W.A. hit, it was neither boring nor repetitive, it was original.