The only open ended sand box game that really sucked me in was Mafia. It had a compelling storyline set in a seductively beautiful entirely credible 1920's prohibition era city. GTA 3 was set in an ugly city and had a poor story, I hated it. Far Cry 2 is set in a lush jungle setting but it lacks the Tropical beauty of the original Far Cry. Even more importantly there are no civillians in this world. Every one you meet totes a gun and 99% of them try to kill you. I guess it is understandable that Crytek choose not to populate their game with the starving victims of conflict but the world feels much shallower for lack of ordinary people.
An engrossing storyline could save the game for me but so far I have seen no sign of it. I am only a few hours in however so things could improve yet.
Far Cry 2 has got pretty good reviews from the critics but player reaction has been mixed. PC gamers who were hoping for a true sequel to the 2004 classic seem to have been disappointed while console gamers who only got a poor knockoff of the original seem to be more pleased.