Got my Copy from EB Games yesterday afternoon and was able to put a few hours into it.  The scope of this game just blows me away.  I was able to jack a little jet at an air force base on the East side of Panau and took a quick spin around the island.  HUGE is and understatement  there is no way in hell I will be able to explore all of it.  Its also way too easy to get sidetracked.  A 3 km trip between 2 missions took me over an hour because I had to destroy a town and small military base on the way.  
I agree 100% completion on the missions can be a real pain.  Took me over an hour to clear out a power plant  stupid power generator hiding behind a couple of cargo containers took me forever to find.  Only really an issue if youre a completionist.
I also wish ammo wasnt so hard to come by.  Hopefully this becomes less of an issue once you upgrade your guns a bit.
Cool little video - makes me wish I would have bought the PS3 copy so that I could share some of funnier moments in this game.  On that same mission you recorded I didn't fire my gun once - it was too much fun using my grappling hook to fling those jeeps off the road.  
Edit:  Hey I just realized I didn't get a GameStop preorder code.  Was it in the box?