I'd say it's a perfect mix of Far Cry 1, Assassin's Creed and Red Dead Redemption... And it has my vote for Villain of the Year so far, this guy is insane!
Now I know this sound like a lot, but it has been called "Skyrim with guns" - should get some people hot and bothered
Here's the awesome opener for those intereste

(Storyline involved of course, so SPOILERS)