Picked the game up on Friday, have may 7 hours of play time with it and have barely scratched the surface of the main story. All I can say about the world is WOW. Stunning, feels incredibly real. A drop in the mud leaves imprints, gets your character and horse dirty. Go hunting and skin a deer and take the carcass? Well that leaves blood stains over your shoulder where you had the dead skinned animal. Voice acting is superb and characters look unique, especially coming from the latest Assassins Creed which has the worst voice acting and so many of the NPC characters you deal with look the same.
Interacting with the world around you is incredibly well thought out, and the relationship with the horse is fantastic. The first portion of the game starts with your gang fleeing from the law up high up in a mountain during a snow storm. You feel the storm, the coldness, everything about it, it is so superbly done. From the tracks you leave in the snow, to the sound and lighting, I have really never seen anything like it. If you like open world games, this is one you must pick up. I will not say it is my favourite yet, but from the little I have played so far it looks like it will be.