>>25038199New Pokémon (although I admit gen 5 was outside gen 1 the only gen where I didn't know the new Pokémon beforehand), great rivals (Bianca/Cheren) who had some character development and some places were really great (Nimbasa). And for Pokémon standards, I liked the plot.
Besides, Pearl was too slow for me and was not a fan of the many new Pokémon hidden until postgame. Also, too many legendaries.
And the original Johto games only got interesting for me when I reached Kanto. That didn't change for HGSS.