I grew up in the 70's and 80's so I grew up loving arcade games so that style of game is definitely my favorite genre. Also a big fan of racing/sports, adventure games (like the old Lucasarts/Sierra style adventure games), simulation games like flight, pool, pinball, puzzle games, strategy and shmups.
You look at that list and it's easy to see I'm not a big modern or current gen fan. The top 5 popular genres now seem to be platformers, rpgs, first person shooters, 2D fighting/beat-em-up games, and 3D action games ala Assassins Creed or Tomb Raider. None of those really appeal to me.