The first people from fansites had a chance to play a nearly-final version of the game:
http://rockstarhq.multiplayernetwork.net/featured/60/
(links to 6 other previews are at the bottom of the page)
It is said that the map is actually bigger than the one of Red Dead Redemption, about 8 square miles and obviously more crowded - one preview mentioned that there are actually only few remote areas. Here's a link to the map:
http://img688.imageshack.us/img688/2640/mapwg.jpg