I think Just Cause 2 is very overrated. I did have a lot of fun just messing around, but eventually repetition set in and there was just nothing else to the game. There were only seven main story missions (with a story that I'm not sure if it was a parody and supposed to be bad or if it was just plain bad), and being forced to go around causing chaos got really boring after a while. Once you've destroyed one base, you've destroyed them all, and what's the point of exploring when everything looks the same? The side missions for the criminals were equally boring, especially the nine identical missions where you take over bases.
At least when I get bored of messing around in Grand Theft Auto (and at least those games have more interesting maps), I have a decent story and fun missions to get back to.