My favorite sandbox games of all time.
The web-swinging mechanic is some of the most fun I've ever had in gaming, let alone sandbox gaming. Let us not forget that the story is based on an excellent superhero film and the combat isn't really that bad. And, of course, the web swinging. Exhilarating and fun from start to finish. see more on Spider-Man 2
There are lots of things I could say about this game, like how the combat could use some tightening up, how buying things is a hassle, how the story is crap, and how the travel time can get annoying, but I once destroyed an oil rig by throwing a jet into it and ejecting at the last second, then I attached a government soldier to a gas tank, shot it, launching him and the tank off the oil rig where it subsequently exploded, sending him to a watery grave below. This game is amazingly fun. see more on Just Cause 2
Red Dead Redemption is not only well written, it's a fun tribute to Spaghetti Westerns that does occasionally take itself seriously, but knows when it's appropriate to keep things light and fun. The gunplay seems too easy occasionally and the side missions can occasionally take too long, but there's enough to do in the world to keep you busy for a long period of time. see more on Red Dead Redemption
What can I say about the Sly Cooper series? Fun aesthetic, good gameplay, varied missions, and in this installment, neat little sandbox worlds for you to play around in opening up after you finish an area. Very fun game. see more on Sly 3: Honor Among Thieves
This game isn't as light in tone as some of the other games on this list, but it's got fairly interesting characters, some fun powers to use in combat, some fun and varied side missions, and it's not a game where a super-powered space marine shoots at aliens from a piece of chest-high wall. That last one by itself should be enough. see more on Infamous