I just didn't buy his transformation into a "warrior". What the other games had where playable characters with military and mercenary backgrounds, which gives believability to their actions and growth. Jason Brody was pretty much a "daredevil" and "thrill-seeker", with no military experience (having never killed anyone before the events of the game); then by end of the game he's this super badass who wiped out countless pirates, paramilitary soldiers, knows how to handle every weapon imaginable with ease, and managed to lone wolf his way into retaking the Rook Islands. I just didn't believe it.
I know it's a game, but they talked up this focus on narrative and about Brody's transformation. They just never really gave believability to his evolution, expect for that his "tattoos" gave him power. That was it. No crash-course training sequences, just buy a gun and you're already a badass. It just wasn't legit. In the way that Jack Carver in FC1 and the Mercenaries from FC2 were.
Yeah there was way too little story to make the transformation actually believable. He kills a few guys and immediately turns into a dick to his friends. It seems like many of the insanity stuff has been pared down last minute (for instance in the story trailer you can see
Vaas have one of your friends put a gun to his head, shouting kill me kill me, before calling him weak and killing him