I'm only about halfway through the main story, in Chapter 4. A couple of things I'll say:
It's a technical masterpiece. It's graphically pretty awesome, though not revolutionary. It's just kinda the summation of the generation's work, kinda like GTA5 was for the PS3/Xbox 360 era. It has more detail than ever before, and that's one thing the "new" consoles added the ability to have; more detail. RDR2 is the unquestioned king in that regard.
Their mechanics DO feel like they are slightly aging, but they aren't in need of anywhere near the overhaul that say, Bethesda games are. But another one or two titles like this, and Rockstar will be entering that territory. The whole "go to destination while listening to NPC pontificate" formula is a bit dry. Not that it can never exist -- the Witcher 3 does it, for example -- but once again, studios need to look to the Witcher 3, because it's the King right now. No one has done it better than that 2015 title. Meanwhile, Rockstar seemed to take more of it's interface and visual design cues from 2013's The Last of Us, if you ask me. It has a lot of that feel, and even a lot of that level of graphics and look, except it's able to do all that in an open world, not a linear game.
The writing/story, voice acting and dialogue leaves a bit to be desired; but that's kinda always the Rockstar deal. It's not NEARLY as bad as, again, Bethesda, which at this point is like cringe-worthy how mechanical, uninspired, and corny it all is. Rockstar has too many lazily written moments, too many lazily written dialogue lines, too many lazily delivered dialogue lines, but they feel worse than they are, in comparison to the rest of the industry, because of how good everything else is. Arthur Morgan, IMO, is excellently written and excellently delivered. So is Dutch for the most part. Some of the side characters, though, even John Marston, feel like they fall a bit flat.
And the regular NPCs, like quest characters, my god, some of them are not good. They talk like they are speaking how a 20th century high school student THINKS a 19th century person would talk; that is, in ridiculous platitudes and generalizations. Even Rockstar's satire here is empty: their mocking of the KKK, Eugenics advocates, suffragettes, gun fanatics, politicians, race and sex in general, the satire is empty and stereotypical itself. The Eugenics advocate says, plainly and shallowly "You are a fool for thinking that colored people are equal! Good day to you sir!" He has no more complex argument than that; it's almost farcical. The complexities of the eugenics argument are so much more ripe for a DETAILED skewering, something that might be funny to both sides, in today's political environment, but instead Rockstar punts with "This character just hates everyone. Look how dumb he is!". Not even fun to interact with this character.
Overall, how does it grade? Does it hold up to RDR1? I'll say yes.
My overall grade is leaning towards like 9/10 or higher. It's a tremendous work. IMO, it's a blast to get sucked down the rabbit hole of it's hyper-simulation. Yes, it's time consuming. Yes, it's a chore at times to walk across your camp. To not be able to fast travel. To whistle and your horse is too far away (ironically, people mocked the Witcher and RDR1 for the insta-spawning horse when you whistled, so, you know, damned if you do, damned if you don't). But at the same time, it's also obvious those were conscious, deliberate design choices that the company was specifically willing to live with, so I'm not faulting them for bad design. It's just not everyone's cup of tea.
Does it compare to RDR1? Well, I think I'd have to say RDR1 was better, but RDR1 was also an all-timer. And I think from many (most, really) perspectives, RDR2 is objectively "better," but SUBJECTIVELY, RDR1 has the newness edge; RDR1 did it FIRST. Which is why it scores better, why it's remembered better.
What RDR1 was a first for many open worlds, it was a first for the Western Genre (a game of that quality as a western was unheard of), and John Marston was such a good character. RDR2 is BETTER than RDR1 in almost all regards, but not enough better and not enough different that it scores better marks, because it's essentially duplicating and cleaning up a lot of what RDR1 offered, so we feel like it's repeated, and the repeat nature of it loses some of it's desirability. But let's not forget: RDR1 had a lot of fucking slapstick, cornball characters, a lot of real bad dialogue from guys like Seth, Nigel West Dickens, Irish, Sheriff Johnson's deputies, the Mexican Rebel leader was atrocious, and the entire Native American storyline with Dutch at the end of the third act felt rushed and glossed over. I play that game barely remembering that Dutch is the ultimate bad guy (even though his final scene is pretty satisfying); but Bill Williamson seems like the main draw of most of that game; and Javier Escuela is barely explained at all (also side note: Escuela is excellent in RDR2, a dramatic imrpovement; while Williamson is not so much).
Long post summed up: I think RDR2 is great. I will buy it again if it comes out for PC. I will play it all the way through again. It will crack my top 10 or so games of all time for sure (that's another fun topic, post your top 10 games all time). It's right there with RDR1, Skyrim, Last of Us, the Uncharted Series, the Witcher 3, it's in that conversation.
But it can be all that, and it's still fair to feel like it falls a little short of expectations. I wish the world was bigger (amazingly enough. I actually feel like it's a little small; but then, I haven't opened up New Austin yet. Also, Why the fuck remake new austin, but not Mexico? Seems lazy. They better patch Mexico in). I wish some of the dialogue was a little better acted and delivered. The story is ok, but the mechanics need refreshing soon. It's great.... but it's not revolutionary like the Witcher 3 was.
That's my take. Love it. But I can see why others are left wanting something a little different.