The older games are actually some of the games I like the best! I love pokemon Crystal, and Emerald is possibly my favorite game of all time if you consider gba games to be old. I love Emerald for bringing us the battle frontier, and hope it comes back in the Sinnoh remakes. Also as much as I love Oras, especially the Delta episode, I think the main story for Emerald is even stronger because both teams are your enemies.
Even though I enjoyed playing HGSS, I'm one of those people who prefer exploring the simpler more intimate gen Johto of gen 2 to the remake. I like having pokemon follow you in HGSS and the more developed post game, but If I had to choose I go with Crystal because of Kris, the gs ball, the odd egg and I think a more interesting climax when you finally obtain Suicuine.
I don't mind the gen 1 games either. By Yellow I think the front spites are mostly appealing. Also it's cool to have those anime references like battling Jesse and James, and getting your own Pikachu to follow you and inreract with. The glitches are also a joy to explore! And the music in the old Kanto just has a little more edge to me for being so spartan. For those reasons I prefer even Yellow to frlg.