Likes:
-The music composition. (More people mentioned this than I thought would. Yay! ^.^)
-The interesting Magma/Aqua rival teams story line. Perhaps the leaders weren't as... fierce, but the philosophies each team had actually made the story more interesting as opposed to Team Rocket just stealing Pokes to make a quick buck.
-The elegant feel of the 3rd gen contests, as opposed to the 4th gen's hyper-kawaii atmosphere
-The scenic routes, and the scenic cities
-The glass-blowing house and the introduction of the color flutes
-Secret Bases
-The starters, Blaziken especially
-Diving underwater. Bring that back please, Gamefreak!
-The creative way to find and unlock the Regies. Reading Unowns: pushover and boring. Decoding Braille: a bit harder (you actually had to look in a book or online!), and much more fun and creative.
Dislikes (Since I started getting into Pokemon in the 3rd gen, my dislikes are rather strange and knit-picky):
-Not being able to choose who you were in your Secret base
-Drake was flippin' hard compared to the rest of Hoenn's E4.
-Blaziken's slow speed, especially when trying to flee from wild Pokes (I never wanted to see another stupid Linoone again! Or those Golbats on Victory Road! Ugh!)