Pokémon Gold and Silver were meant to be the final Pokémon games; imagine that. They were groundbreaking and introduced a lot of crucial changes that are now foundational for the current games, such as the Special split into Special Attack and Special Defense, the use of time (ie. day and night and their relevant events), Berries, breeding, held items, genders, and Shinies (amongst other features you can find on the Bulbapedia page).
The above commercials, which also includes Crystal, brings the focus on children playing rather than the weird group of adults in the first ever commercial. And technology has evolved significantly in those 3-5 years (it’s Japan, after all). The music is superb, the tech looks awesome—even now—and everything looks… fun. Playing your favourite games with your best friends. That’s what Pokémon is all about!