Big Boss' crime was revealed in the very first 'Metal Gear' anything that Kojima has made, ie. the Metal Gear on the fucking MSX. He fucks over both Gray Fox and Solid Snake over the guise of trying to stop Outer Heaven, when in reality he's the one controlling it. He's an evil cunt sacrificing soldier's lives to further his own goals. Then MGS3 cleverly reused this by showing that the whole reason he became a jaded cunt is over the Boss being sacrificed by the US government and going along with it - technically because she treasured loyalty the most, but it's implied she was used so many times by the United States she was tired and willingly gave her life.

BB then stews for the next 3-4 games (and OP is right, fuck all happens and Big Boss is usually portrayed as a heroic figure because Kojima lost the plot) and finally breaks and does the same shit to someone else for the sake of taking over the world. Problem with V is that it just rehashes MG1 without doing anything interesting + it adds a bunch of useless, unncessary dumbshit, like:
>by the way, in Tselinoyarsk remember that moment where BB dropped his US-made mask and vomitted on the ground? actually Skull Face was in the background picking up his piss and shit
>by the way, BB actually could run Fox Hound and fool everyone because big medic was a brainwashed body double of his and he ran outer heaven as a proxy agent
>by the way, the cobras could shoot bees out of their mouths because of ancient parasites
>by the way, the 'good' parts of BB's army - MSF - were kind of erased because a bald cunt with burned skin killed everyone and made Miller a jaded cripple and then died to his own Metal Gear while doing absolutely nothing of note afterwards

tl;dr la creatividad huffed his farts so much he became an insufferable retard who only writes mediocre shit now and has no editors left to challenge him in creative ways