I bought Red Dead Redemption, but got way too engrossed in Just Cause 2 to start playing it. It's easily one of the best sandbox games I've ever played.
I never bought JC2, but I rented it. It was really good. The physics aren't exactly completely realistic, but they're decent. It's definitely good enough to buy, if you have the money... =(
--------------------------------------------------------------------------- In the end they will lay their freedom at our feet and say to us, 'Make us your slaves, but feed us.'
The missions can be pretty boring, especially since most of them are just the same thing in a different setting.
Everything else is fantastic, though. Physics are good, vehicles control well, and the map is HUGE. With all my playing, I still haven't even covered half of it.
--------------------------------------------------------------------------- In the end they will lay their freedom at our feet and say to us, 'Make us your slaves, but feed us.'