I've been playing it and it's quite enjoyable. I personally love open world games (Horizon Forbidden West, Marvel's Spider-Man, various Assassin's Creed) and this is right up my alley. Some say the world is bland, I think it looks amazing.
There's not a lot of NPC's in the open world, but there is an explanation as to why. If you like collectible hunting, then this is the game for you. I also enjoy the combat and find it pretty unique. There's a ton to do and a vast area to explore. It's just fun to me.
That all being said, I get why the demo might have thrown people off. I started getting weird vibes when people said it sucked, and I initially wasn't going to try it. I did and fell in love with it immediately, so anything negative from review sites really didn't affect my judgement. It just gave me a better understanding of what I was getting myself into.