But my favourite game? It damages my brain to try and boil it down to a definitive.
The game I've completed more than any other is Half-Life 2. I still remain seduced by the atmosphere of that world, all that fannying around with the Gravity Gun, and the constant barrage of ideas, but I'm done with it now. As beautifully designed as it might be, it's stating to show its age next to current-gen titles, and I'm over-familiar with its tricks.
As I've stated before, the game I've had the strongest emotional connection to is The Last of Us. The story might be slight, but it engaged me. It involved me. I've never felt like I cared what happened to a games character before it, but I've played it through twice now, and I know what to expect. I don't want to play through it again: that big shock at the end of the second act would lose its impact a third time. Its narrative linearity is, ultimately, to its detriment.
The game I've played the most is, probably, either COD: Modern Warfare or Geometry Wars: Retro Evolved - the former for the online play, the latter for obsessively trying to beat my high scores. These days I rarely play online, because most of my mates now have better things to do, and though I'm still occasionally playing Geometry Wars 3: Dimensions, even that has lost its hold on me.