As I'm strictly PC, I've never played V before, so these are first impressions on the whole thing.
The world is amazing - although I'm aware this has been said many times before for lesser titles, we must be converging on actual photorealism/reality now. Some contexts - tree density - aren't as good as others, but otherwise it's pretty incredible.
Technically it works great, although I have a reasonably good PC.
As for the story mode, hmm. I've got a little past the point of access to all three characters, and so far it's a bit by-the-numbers, even though I was looking forward to exactly what GTA does. It feels a bit like a reboot of GTA:SA, which of course it is to some extent, and is fine if that's what it is, but it's just a bit too close.
Because the last games were so great, and partly because it's been 7 years (FFS), I feel a bit like there's a pressing requirement on me to try and extract brilliant times from it, if that makes sense. It means I'm always thinking, 'what if I've missed something', or 'what's best to do next', rather than just exploring & letting it flow.
So far it hasn't really shown off what the engine can do - the magic of GTA is often in surprise set pieces & variety, whereas other games just use much narrower capabilities. There are a couple of exceptions, like pulling/pushing large objects with a car, but not much else yet. Maybe it'll come.