It's incredible.
After you start to get to grips with the controls and inventory you just get sucked into the amazingly detailed world. I spent an hour today just putting a mark on the opposite side of the map and using the cinematic view/follow path combo. It's absolutely breathtaking.
The biggest mistake so far was the first couple of hours which in comparison to the 'main game' were so bafflingly slow, cumbersome and banal.
I am beginning to worry myself whilst playing though. It appears to have turned me into some kind of wild west version of Ted Bundy. I'm constantly finding people out on their own, murdering them, robbing them, hiding their bodies and selling their shiny things to the fence. I think I have issues ?