1. First Person Shooter/Third Person Shooter. If you can get away with it, just say "Action", because I rank action/adventure platformers pretty high also. Some of my favourites within this group are those that can successfully implement certain elements from other genres, like for example Deus Ex had RPG elements.
2. I play for storylines. That's why I mostly stay away from multiplayer games: they're offer no incentive to progress other than the sheer hell of it, and to compete. That's just not my thing, I don't like competition when playing games. The thing that really makes or breaks a game for me is the storyline, no less than the gameplay itself.
3. I have nothing against most game genres, except sports games, racing games and highly technical simulators (mostly flight simulators). Like I said, anything with a story can potentially appeal to me, from graphic adventure games (some of my favourites fall into this genre) to RTS games. Anything that's just sheer progression, with no plot, like sports games or driving games, isn't my thing.
4. Not really. I tried one or two for various lengths of time, notably Dark Age of Camelot a few years ago and recently World of Warcraft, which I played for maybe 3 months total. But these games need to be played socially in order to make it a rewarding experience, and I like to play solo. Which is why I prefer single-player games. Being in a good guild/clan helps, but eventually the treadmill becomes repetitive. If the game is designed well, it can mask the repetitive nature of the gameplay a bit, which WoW does pretty well, but in the end you're still doing the same 3 tasks over and over again.
5. See Question 4. I played WoW for a few months about a year ago and re-activated by account maybe three months ago, though I only played for about a month then just stopped.
6. There are some redeeming features. First of all, that the world is persistent. Also, I really like that you can customize you appearance, which is rarer in singleplayer games. You get invested in your character, since he evolves the more you play. Better equipment, better skills and so on. That's the aspect, I think, that appeals to me. Character development.
edit: please cite my name as Hugh Jass.