for the past couple years whenever I was feeling nostalgic for old pokemon rather than digging my gameboy original and looking for batteries I'd just play Pokemon leaf green and never really found my gameplay desuire satisfied; but ever since getting pokemon blue to work on my cellphone I've realized that the original games have a certain quaintness on the GB that the graphics of GBA games and beyond have not been able to copy.
That being said, I am also playing Pokemon Silver, emulated (I own original copies of both blue and silver so I don't think emulating them is a bad think), but I've had the same game running for maybe half a year and slowly working through it again- really like it but it's such a massive game.
Also I find in addition to fullfilling feelings of nostalgia of my childhood they kind've feel like new games because when I was younger I generally stuck to one basic party shape (Blastoise, Mewtwo, Raichu. Ninetails, Pigeot and Nidoqueen - all with uber attacks) but now I've been changing the party dynamics and using more strategy and choose Charmander as my starter which I have never done before; no offense to charmander I just REALLY like Bulbasaur and Squirtle (who made the first gym easy!)