I watched it last week and treated it like a miniseries, splitting it up across 3 nights. I read the book when it first came out so I kind of knew the story but I forgot some of the details.
I liked it but didn't love it. I thought Lily Gladstone was excellent as Mollie Burkhart, and Leo was pretty good in his role, but Robert De Niro felt really out of place to me.
I think De Niro acted the part well, but the entire time it felt like I was watching Robert De Niro basically play Robert De Niro. That seems to be a minority opinion because I see everyone else praising his performance, but I think I would've enjoyed the movie more if someone else had been cast as William Hale. Also, De Niro is 80 and I think William Hale would've been 45-50 range in most of this movie. That felt a little weird to me because I kept wondering how much money this old man could possibly need for the short rest of his life, but then the movie tells us he lived another ~35 years. It wasn't even close to matching up, and I know Scorsese and De Niro have a strong history together, but I think this casting decision took the movie down a notch for me.
I also think, having read the book and knowing how the story would go, there was a little less shock in the development of the story, so David Grann beat Martin Scorsese to the punch. I suppose you can't blame Scorsese too much, except that I have a hard time calling it a masterpiece when he's telling a story that's already been told quite well.