I just finished the "main story" and I have to say, this game was fantastic. It did seem like the last part was a bit unnecessary (spoilers: Micah fighting with you was kind of ridiculous especially since it was already implied that Dutch and Micah didn't care about fighting you or going back for you and were just running away, I really wouldn't have minded if it was just an endless shoot out to buy time for John like in Halo Reach, although I have a feeling the writers kind of wrote themselves into a trap where it both doesn't make much since for Micah to be fighting you in the middle of Pinkertons being everywhere but it also it anti-climatic to not resolve Micah and Dutch)
I am a bit mixed on how much praise I'd give the actual design of the missions though ... they're almost all very repetitive. And yes, I know that shooting a bunch of guns and mowing down both innocents and police alike is Rockstar's "thing", but it devolved into that too much. A lot of missions would start off very unique, only to become tedious in the end.
People mentioned Naughty Dog earlier. There are quite a few things about this game that remind me about Naughty Dog. Well written chit chat was already a part of RDR but particularly the way characters interact is a lot like a Naughty Dog game. There's also a couple of levels that seem straight out of Uncharted 4. The writing in this game is far and away better than the Uncharted games, which are extremely overrated story-wise. Maybe on par or slightly better than The Last of Us ... it's hard to tell because it's not as linear on that front.
