Released in Japan on January 29th, 2004 in Japan, and September 9th, 2004 in North America, Pokemon FireRed and Pokemon LeafGreen became the second act of the play of the third generation of Pokemon games, following the release of Pokemon Ruby and Pokemon Sapphire, but before the release of Pokemon Emerald. Pokemon FireRed and Pokemon LeafGreen are enhanced remakes of the first generation Pokemon games: Pokemon Red and Pokemon Blue (Pokemon Green in Japan). These games are much more than a simple remake, however. And they helped complete the circle of Pokemon by allowing the last 186 Pokemon to be captured that were unobtainable in Pokemon Ruby, Sapphire, and Emerald.
First things first: This is not the Kanto you remember. Pokemon FireRed and Pokemon LeafGreen have recieved a huge update in graphics, sound, and gameplay features. In fact the only two things you might find similar are the storyline and the Pokemon. Just as in Pokemon Red, Blue, and Yellow, you play as a young trainer destined for greatness who has to face off against the 8 famous gym leaders of the Kanto region in order for you to face the Elite 4 and the Champion Lance.
The various twists and turns of the original games's plots are also present, which means the return of the evil group of Pokemon thieves known as Team Rocket. Using the Celadon City Game Corner as a base of operations, the group not only takes over one of the largest companies in Saffron City, but also disturbs the tombs of many a Pokemon in the Pokemon Tower located in Lavender town.
All the Pokemon, TM/HMs, Items, Attacks, and Stats have all been updated to third generation standards. The game introduced a handy help feature that sadly wasn't carried over to the next generation of games. Pokemon FireRed and LeafGreen also debuted the item known as the VS Seeker, which allowed the trainer to rebattle opponents that had already been defeated once before. The game also allows for previous movesets through the use of special Move Tutors, most of which are based off of Pokemon Red, Blue, and Yellow TMs.
The biggest addition, however, is the newly added Sevii Islands. The Sevii Islands are a cluster of seven different islands far out at sea, which are first reached after beating the 7th Gym. More islands open as you progress. These islands contain a side quest which allows the trainer to then trade Pokemon with Pokemon Ruby, Pokemon Sapphire, and Pokemon Emerald as well as catch many types of Pokemon that weren't originally introduced until the second generation of games. Consider Pokemon FireRed and Pokemon LeafGreen to be completely new games that happen to carry with it the flavour and spirit or the original.