The high drama of family strife, conspiracy, betrayal, and power, played out with life or death stakes. Or at least, that's what I enjoy about it. It's very operatic. Plus it's got a number of excellent performances and an excellent soundtrack. And as an aside, it's a rare example of a movie being far better than the book it's based on. Fond as I am of the novel, there's a lot of shit that the movie rightfully excises (in the novel, Sonny's unnaturally large penis is literally an integral part of Lucy Mancini's subplot.)

Also, particularly when combined with the sequel, Godfather shows a mythologized, multi-generational rendition of the Italian immigrant experience. More broadly, it's a cultural artifact of 70s America that reflected a growing sense of otherness among so-called 'white ethnics' from the socially dominant WASPs, and a rejection of the assimilationist tendencies that had supposedly characterized the immigrant experience prior to that point.

None of this is to say you have to watch it. If it isn't your thing, then it isn't. I hate when people insist that a movie is essential somehow, and that there's something wrong with you if you don't like it. I just figured I'd share a bit of what I liked/thought about it.