Pokemon games are a very popular game franchise, pokemon is actually the third highest grossing game franchise with almost 300 million gross profit. The majority of the pokemon games follows the story of a young pokemon trainer that has just moved into a new town. Your character leave home and explores one of 7 regions (depending on the generation) and catch creatues known as pokemon. There are 7 generations in total as of now with between 71 and 156 new pokemon for each generation. There are 18 categories that pokemon fall under called "types", all pokemon come under either 1 or 2 types depending on the pokemon. Each type has some weaknesses and strength and even some immunities to to other types(ground does not effect flying). On average pokemon games from the main games take around 120 to 200 hours to 100% complete. This includes the main story, all extras, and collecting all the pokemon in that game.
Some of the more popular pokemon games include, Pokemon Fire Red, Pokemon Ruby/Sapphire/Emerald, Pokemon x and y, and Pokemon Sun and Moon. These are games that pulled in a huge amount of gross profit for the franchise, to fuel the continued growth of the franchise.