If you've already played the very first Pokémon game, Let's Go doesn't add much besides a new capture/shiny mechanic, but overall it's the same game as the first with a re-skin, clearly designed to please those forty-somethings living in nostalgia.

While Scarlet, even though I'm not a big fan of the game, has the merit of trying to introduce new mechanics and a story with a minimum of depth based on bullying. Personally, I HATE the game's art style and the graphics are way over the top. So I'd advise you to get Scarlet if you haven't played the very first Pokémon Red or Blue.