Hope restoredfrom Kotaku reviewer
I'm not even close to finishing the game but I've skimmed the IGN/GameSpot reviews and I'm starting to suspect that there might indeed be a hidden "true" ending that GameSpot saw but IGN didn't. (That'd help explain why GameSpot raves about the story while IGN says it's disappointing.) Just guessing, though. No spoilers here, but from what I've seen so far, some things MGSV are ostensibly optional but should probably be played or else it seems like you'll miss out on big things.