The Pokemon Company recently put out a new trailer for the upcoming Pokemon: Let's Go, Pikachu and Pokemon: Let's Go, Eevee that shows off a few things that you couldn't do the first time through Kanto...or the second time if you count Gold and Silver...or the third time if you count Fire Red and Leaf Green. Besides being able to customize your trainer, you can now customize your starting partner a bit including clothing and hairstyle. Also, both Pikachu and Eevee can be male or female. Male Pikachus will have a straight-ended tail while females will have kind of a heart shape to it. Eevee's tail pattern is similar with a female's tail having the tan part in the shape of a heart. The trailer also shows off the ability to ride around on larger Pokemon such as Arcanine and Onyx, something that was recently introduced in more recent generations.
The games will also bring back some familiar elements such as gym battles (specifically showing off Brock and Misty), Professor Oak, and the Bug Catcher Kid who likes shorts because they're comfortable and easy to wear (sorry, I had to make the joke). Another video I saw online that wasn't from an official Nintendo YouTube channel also briefly showed Jesse and James from Team Rocket, which shouldn't be a surprise seeing as how this is a remake of Pokemon Yellow which included Jesse, James, and Meowth as it was more closely related to the anime.