I was discussing this with my elder son this morning during our walk into town. He's an avid gamer, which is odd 'cos he does have a girlfriend, and he reeled off all sorts of names that I'm only vaguely familiar with.
Up until about 10 years ago I played a lot myself, and indeed still do occasionally, although I've always tended to just play one game at a time, and the 1st anniversary of my being stuck on Resident Evil 5 is fast approaching - but anyway for me nothing has ever come close to the first Playstation game I ever played for any length of time, which was the original Doom - I never played the iconic PC version, and I think the Playstation effort was actually a combination of the first two in the series - fantastic game and as a result of the memories stirred I shall be up in the loft tonight looking for game and console.
I know the graphics are awful by today's standards, and the sound too (although incredibly atmospheric) but I never enjoyed a game as much again