I've tried to watch it several times but always shut it off.
It's a movie that's constantly aware of itself and tries to push that onto the audience through self-conscious directing—which explains all the nepotism in casting too—and hat makes for disengaging storytelling and characters. And then there's the cinematography that tries too hard, so it's more a technical exercise than an effective one, but was successful in its era for that uniqueness.
Not to nrglect it's an awful portrayal of organised crime, much like The Hurt Locker is at war. And Luca Brasi, ugh. It's just awful.
In the modern day, I've understood the trilogy to be a go-to for "movie buffs" that are vulnerable to ad populum.