Mercenaries 2: World in Flames was pretty much ignored at the time of release. Sandwiched between GTA IV and Saint's Row 2, I guess it was one sandbox game too many.
But it's actually a
really good game. It had an amazingly comprehensive damage system that let you raze entire cities to the ground with no indestructible buildings - you could even bring down skyscrapers. (Compare to GTA IV, where you can't even take out some railings.)
It also did a great job of depicting a war-torn Venezuela, with the country gradually descending into anarchy as the action heated up. You really felt like the population was reacting to the escalating crisis, with people fleeing in droves and causing traffic congestion amidst all the fire and smoke. Granted, the enemy AI was pretty crappy and the cut scenes were nothing special, but despite these faults, the game is an underrated gem.