Assassin's Creed 4: Blackflag for Free (PC version). Ubisoft is giving away the best AC game they've ever made for free. Don't know how long this'll last.
Honestly this is my favorite AC game. I've played AC 2, AC 3, AC 4, a few hours of AC Syndicate and watched a Let's Play of Rogue. Out of all of those the only one that I really, really enjoyed from beginning to end was Blackflag. Highly recommend getting it, even if you don't have a computer that can run it (just so that it's in your library for the future).
Unlike AC 2 and 3 you don't have to play previous games to really enjoy Blackflag. For the real life portions of the game you play as an unnamed researcher/game tester who's delving into the past to get footage/info for a fake game. Yeah, the Templar stuff is still there, as is the Sage stuff, which if you never played any of the other games you might be a little confused about all that, but the actual pirate simulation/historical portion of the game is awesome and the real life stuff is largely ignoreable.