27 here, started playing in the early 90s with our 286 computer. My first games included classics from Sierra such as Space Quest, Leisure Suit Larry (I know, not exactly appropriate for a 6-year old, but that man and his suit taught me a lot about the birds and the bees
), Quest for Glory etc. Hard to say which is my favorite genre or niche.. perhaps RPGs, especially fantasy ones. My most unforgettable game so far has probably been Baldur's Gate 1, and to a lesser extent its sequels. There was something magical about that game, as I had only played those old D&D gold box-games before I was introduced to it. And then I am tossed into this utterly captivating fantasy world with an awesome plot, musical score and gameplay.. I was instantly smitten. No game since has matched the feeling I got from it, not even Skyrim. I was 14 when I first played it and I still find myself humming the soundtrack sometimes and feeling nostalgic.
Other classic games spring to mind, too.. Wolfenstein 3D, one of the first quasi-3D games, shortly followed by Doom and Doom 2, both of which I had an immensely good time with. And then came Duke Nukem 3D; I played the hell out of that one during the summer when I turned 12.
Other games that I've enjoyed over the years include the GTA series (especially San Andreas, as someone above said), Black and White 2, Lord of the Rings: Battle for Middle-earth 2, Gears of War, the Halo games etc. I tried to play Morrowind but couldn't get into it for some reason. The world felt too sterile and alien, somehow. But I did enjoy Oblivion!