Mass Effect 3
When the ending of a game makes you sob like a baby for the characters you've come to love, the relationships you've formed and the amazing things you've accomplished... you know you've found a very special game. Mass Effect has, from the very beginning, completely immersed me. I liken it to a good book (or series of books). You start to become part of the story. You get emotionally invested in it. That's what makes a great game, in my opinion anyway.
Thanks Bioware. You had me worried for a while, but when push came to shove, you were still able to "take me there" and I don't think you could have made it any better. Now, to import my "bad" character and see what I missed!
Oh, and Garrus, now you have me thinking... what WOULD a Turian/Human baby look like? Hmm, interesting. Any of you artists out there come up with any concept ideas, let me know. I just know this will be the question that keeps me up at night. :P