AlKim: Steam says I've put 31 hours into Just Cause 2. That includes a playthrough, some random fucking about, a friend playing for several hours and quite a lot of boredom. Blowing things up for no reason is satisfying in short bursts but gets repetitive very quickly - and let's face it, all you ever do in JC2 is blow things up. The world is massive, quite pretty, but uninspired; the Grand Theft Auto and Saints Row sandboxes are more varied and alive. The story is ludicrously bad, not that you're supposed to care. The game has been praised by many, but not me. Buy it if you want to, but do yourself a favour and avoid the DLC. You won't be missing anything. EDIT: By the way, I'm not trying to say the game is shit. It most certainly isn't. I'm just not sure whether I'd call it good either.
I think the big draw is supposed to be all the stunts you can do. Stuff like driving a firetruck into a fuel tank, parachute out at the last minute before the explosion, grapple onto a motorcycle to make your getaway, and attach your motorcycle to an airplane.
Except I'm not skilled enough to pull off all those stunts, so I kind of miss out on a chunk of the experience.