Played for six hours today and I'm loving it. I've only done the first couple of story missions (enough to unlock the wingsuit, basically), and I've just been zooming around destroying bases and coming to grips with the new mechanics. It feels like exactly the improved sequel to Just Cause 2 I always wanted. Much as I adore that game, I already feel like I could never go back to it because JC3's wingsuit is just so good.
Wingsuit's a gamechanger, I absolutely love the sticky rockets (just like Batman: Under the Red Hood!), and the new realtime checklist thing that lets you know exactly what you need to destroy to completely take over an area is such a great addition. Vehicle handling is way better than JC2, too; still not exactly great, but I feel like I just need to spend some more time with it to get a feel for the handbrake turns, whereas JC2's vehicles were just a lost cause from the very beginning. I still haven't even unlocked the Rebel Drops or Fast Travel, so I suppose I should do a couple of story missions.
I can totally see why it's getting 6s and 7s from reviewers, because it is ultimately the same open world checklist-ticker that JC2 was. It's hardly pushing the genre forward, and if you didn't like 2 then 3 is still going to do nothing for you. For me, though, it's everything I wanted; amazingly fun basic gameplay and a big ol' playground to go nuts in. And, randomly, David Tennant!