I've seen people pretend elsewhere
Anyway, these games are based on the games of Gold & Silver that were released back in 2000. They feature many of the original 150 Pokémon as well as the Johto 100 Pokémon before you beat the game.
It has two regions, Johto and the original region Kanto and features the continuation of the Team Rocket storyline in addition to the new trainer bits
It's well worth it, I'd happily say it's the definitive Pokémon version