This is a list of all the major changes between the original G/S and HG/SS.
All Pokemon from Generation 4 are obtainable.
All Pokemon are able to follow you like Pikachu did in Pokemon Yellow.
All the music has been rearranged to better suit the DS’s capabilities, you can still access the old music via a key item.
The Team Rocket executives have been redesigned to have their own persona rather than looking like another grunt.
All berry trees have been turned into apircorn trees, berries now can only be bought or won.
Many gyms have had their puzzles and designs changed.
The HM Rock Climb has been added allowing access to new locations.
Instead of the Fuchsia City Safari Zone being just closed they replaced it with the Pal Park.
The Battle Frontier has been added into the game.
The Pokedome has been added into the game.
The new Safari Zone has been added into the game.
Routes 47 and 48 which lead to the new Safari Zone have been added into the game.
The Fighting Dojo now acts as a place where you can have a rematch with an old gym leader from either region.
Route 23 is missing since it’s been merged with Indigo Plateau.
You must fight your versions Legendary in order for the story to move on, in the original they were optional.
You encounter all 5 Kimono Girls throughout your journey and help them out in various of ways. Also you must defeat all five of them in order to fight your legendary Pokemon.
Legendaries from other regions can be caught depending on your games version.
Trainers in all parts of Kanto now can give out their phone numbers.
Your Pokemon can be moved to the Pokewalker.
Via a Celebi Event you are able to go back in time and fight the previous leader of Team Rocket Giovanni.
