I got it just before it came out (released on the 29
th here in Europe, imagine that!) and I've enjoyed it so far. The best parts are the outpost assaults, IMO. There's something deeply satisfying about staking out an outpost and then executing a flawless takeover by killing everyone in just a few seconds.
That one mission where you torch a drug plantation with a flamethrower while reggae music plays is also hilariously awesome.
The wildlife is a pretty interesting addition as well, although they could have given them better AI. Right now they're either blindly attacking you (through automatic rifle fire) or running away from you. Also echoing the dislike of quicktime events. They work decently well when they are just "mash [button] to stop getting chewed by crocodile" but prolonged sequences of quicktime events? No, thank you.
About the narrative, I can't say I care for it either way. It's not bad, but certainly not good either. Most characters are pretty flat, your friends are weirdly okay with you becoming a one-man murder machine overnight and just pretty blasé about the whole ordeal. There are a few points where they show some emotion, but then they just go back to not caring again a few minutes later. The villains are pretty neat, though, they're obviously bat-shit crazy, some more than others.
Even your allies are pretty crazy. The CIA guy and his German friend comes to mind, I wonder if he really is a CIA guy, or if he's just freelancing and pretends/believes he is.