I can't get you out of my head. Boy, that song is all I think about. I call it the "ding song," and it has been haunting my dreams for over a year.
Anyway... XCOM: Enemy Unknown was my personal GOTY 2012, and the Enemy Within expansion only makes it better. With new technologies (mechs!), a nuanced new human enemy faction and bags of content, it makes the campaign feel like a completely new game. If you've yet to play it, Green Man Gaming will save you a few quid with their GMG25-0YUM5-VKMVU voucher code.