It may overstay its welcome after over two dozen hours.
Just Cause 2 provided me with countless hours of unthinking fun, but its chief downfall is the fact that size doesn't actually matter. It has an astonishingly huge map, but a dearth of interesting content and variety imbued within this map. To that I think Just Cause 2 is a good textbook example of a fundamental weakness of open world games. There's not much to the world aside from collectibles and countless things to blow up that you can find in any of the game's villages and towns. When variety and carefully crafted content is thin on the ground, it doesn't matter how impressively large the map is; it becomes monotonous and samey.
But having said that, I very much enjoyed my time with it. It's a good change of pace if you've just come off a long RPG or a game that requires a lot of tactical thinking. Just Cause 2 is decent escapism, and rather cheap these days to boot. If you can acquire and play the PC version of the game, it also comes with a mod that packs in a multiplayer feature that is not present in the base release (i.e. Avalanche did not create the multiplayer mode. Fans did.). Also, it's amazing how much a simple grappling hook makes traversal so much more engaging.
The story is short and laughably awful, but you wouldn't expect anything more from a game that is primarily about blowing things up and being as much of a nuisance as possible to the local dictator. Still, you'll eventually fight the guy on a rocketing nuke towards the end, so there's still much to be entertained by, despite a narrative that few will look back on as anything Shakespearean in quality.