That graph is eerily accurate. I stopped at 9 hours because I realized that hunting was boring, side stuff was a bunch of fetch quests,climbing radio towers was a dumb QTE, taking outposts was the same shit everytime, the crafting system is boring and doesn't reward experimentation and the story is just bland.
I can't figure out why reviewers rated it so high. Truly puzzling.
While I haven't played Far Cry 3 yet so I can't agree or disagree, I would speculate that a kind of "out-of-the-gate" syndrome is going on.
By that I mean, games like Skyrim, where the first few hours are absolutely marvellous to play, so any reviewers out there, mired in their cynicism and drudgery of playing games all day, get hit with the best the game has to offer right at the beginning. After they are left with the best first impressions possible, the gameplay slowly boils off to reveal that it's a bit shallower than it appeared going in, but that rarely reveals itself until well after a review needs to be pushed out the door.
Don't get me wrong, I'm not saying games like Skyrim are bad, nor am I saying reviewers are wrong, I just suggest that perhaps "front loading" is occuring within game presentation.