Well...
I liked the release of Yellow more, cause the graphics of the pkmn were much better then the ones in Pokémon R/B and you could get a Pikachu with Surf, and at the time it was released, I still watched the anime ( yeah, I was just a little boy that time) I was thrilled that you could fight Jesse and James :P at the game, which I thought was very awesome back then.
I was kinda dissappointed with Emerald, it was basicly the same game as R/S for me, I expected more of it. (Rebattling Gym Leaders, other twist in the story around the 2 criminal teams, just wasn't enough for me.)