It looks really good. Watched a couple hours of streams, and the variety is insane. So many completely different locations, so many completely different quests. The combat looks great too. Best part so far seems to be the world: it seems believable and alive. A lot of random encounters at just the right intervals, and they all looked interesting and there was a lot of variety there too. As opposed to open world games like The Witcher 3 where there's a lot of space but it's just filled with copy-paste bandits and monsters, to the extent that it's not a believable world at all.
And there's a lot of story. Rockstar isn't afraid of taking it slow and telling the story instead of spoonfeeding the player constant mindless action, which is also really nice.
Definitely GOTY, really hope they port it soon.