Just Cause 2 is an excellent sandbox game, set on the huge island of Panau. You're there to overthrow the crazy dictator, using any means necessary, and luckily the Just Cause 2 gives you some wonderful tools to achieve this.
This is a third person action game, based in an open world that you are free to roam around doing whatever you want. You are equipped with various guns and weapons, but most importantly a grappling hook and parachute, allowing you to climb up almost anything, and jump off anything too!
Progress in Just Cause 2 is measured by Chaos. The more government stuff you destroy, the more missions you complete and so on, the more Chaos you earn.
The action in Just Cause 2 is as good as you will find in any game. The story is silly, but what it allows you to do makes it worthwhile. Skydiving onto planes and helicopters, strapping enemies to moving vehicles and much more. The freedom Panau give you is impressive and there is hours of fun to be had simply creating chaos outside of the story. Best of all, Just Cause 2 looks great too.