The main difference between Pokémon: Let's Go, Eevee! and Pokémon: Let's Go, Pikachu!, is the starter Pokémon. In Pokémon: Let's Go, Eevee!, you begin your adventure with an Eevee by your side, while in Pokémon: Let's Go, Pikachu!, you start off with a Pikachu.
These two games are otherwise very similar. Both are set in the Kanto region and feature the original 151 Pokémon. The gameplay mechanics are also mostly the same, although there are a few key differences. For example, catching wild Pokémon is easier in these new games than it was in previous entries. These titles also introduce new features such as co-operative play and online battles.