I used to play HGSS until I stopped because it kind of bored me (surprisingly, I guess the games were too long or something @[email protected]). Other than that, I would like to play Emerald again, that's been on my to-do list for a while.
I play, hmmm, let's see: Red, Blue, Yellow (Not very often, but I play 'em a little), Gold, Silver, Crystal, FireRed, LeafGreen, Ruby, Sapphire, Platinum, Pearl, and SoulSilver. Those are my Gen I-IV games. I play all of them, too.
I replay all of the games from time to time. Generation 3 and 4 more then 1 and 2, but there is still some fun in switching to generation 1 or 2 for the sake of mixing up the feel of the battle system.