I just finished the game tonight (21 hours) and did most of the side quests (including securing all 18 radio towers and freeing over 25 of the bases). I also did all the hunting and death quests and maxed all my craftable items. My review can summed up in one word: AWESOME!
The world is open and gorgeous. The openness and size of the world is similar to Red Dead Redemption except it is a heck of lot better to look at (desert is boring). The wild life can attack (just like Red Dead Redemption). The voice acting was top notch. The story was engaging and yet not drawn out too far (which is what I was fearing). The pacing is right and 21 hours to finish felt near too long nor two short. I absolutely loved this game!