So I narrowed it down to Assassin's Creed 3, Mass Effect 3, Dishonored, The Walking Dead and Halo 4. I never beat Dishonored (haven't finished it yet) and haven't beaten The Walking Dead (only own the first episode) so that narrowed it down to Halo 4, Mass Effect 3 and Assassin's Creed 3.
I took the positives from each and compared them to one another: Graphically I felt Halo 4 was the strongest because it took the Xbox 360's graphics and pushed it to levels we haven't seen before, however I felt like Assassin's Creed 3's world was more beautiful just out of sheer scope. The gameplay for Assassin's Creed 3 was the strongest in my mind, however the protagonist was uninteresting and there were quite a few bugs with the release of the game that have yet to be fixed. Meanwhile Halo 4 had two strong protagonists however their secondary characters were weak and uninteresting. The strongest antagonist I felt was Assassin's Creed 3 in Haythem Kenway (God I loved his character) and even in Charles Lee, whereas in Halo 4 the antagonist seemed uninteresting and distant for most of the game. The ending for Assassin's Creed 3 was good for Connor (who redeemed himself to an extent at the end with his character development) but very confusing with the modern day Desmond story arc (unless if you take an in depth analysis of all the Assassin's Creed games), whereas the ending for Halo 4 seemed to be pretty solid, however was extremely depressing (for me) and left little room for a sequel (unless if I missed something).
What about Mass Effect 3? Well Mass Effect 3 won my vote in the end for a number of reasons: The protagonist and the supporting characters are all rich and complex, some of the more memorable moments in the series' history can be found here, the antagonist (or antagonists) are all pretty solid, with the dlc update the ending is a ton better, the gameplay is fun and well constructed, graphically the game is beautiful, and the scale of the game is massive in scope. I hardly see any faults in Mass Effect 3 (they are there but are few) and when compared to Assassin's Creed 3 and Halo 4, I believe Mass Effect 3 to be a superior game.
Unfortunately I was unable to complete Dishonored or The Walking Dead before this time so voting for either of them would of been unfair on my part, and I also haven't tried out the other games that have come out this year so perhaps there are others who are more worthy than Mass Effect 3, but my vote goes to the game that, through my experience, deserves to win.