Pokémon Let's Go Pikachu & Let's Go Eevee was been praised by both old and new fans of the series, but there is one notable absence from the beginning of the game that annoyed some of the fans of Pokémon Red & Blue.
The introduction to Pokémon Red & Blue shows a Gengar battling a Nidorino, which was the same scenario used for the opening moments of the Pokémon anime, except with much better animation than what we saw on the Game Boy.
Pokémon FireRed & LeafGreen also featured an updated version of the Gengar & Nidorino battle, which used the improved graphics of the Game Boy Advance hardware.
Pokémon Let's Go Pikachu & Let's Go Eevee missed the opportunity to show the Gengar & Nidorino battle in HD using the Nintendo Switch hardware and chose to use an opening cutscene that showed your starter Pokémon inviting you to follow them into the TV, at which point you meet Professor Oak.
There is still a reference to the fight between Gengar and Nidorino at the start of the game, as there is a poster in the main character's room that shows a Pokémon battle between the two Pokémon using the same format as the kind shown in Pokémon Red & Blue, with Gengar in the foreground and Nidorino leaping towards it.
The staging of the battle between Gengar and Nidorino is clearly something that the developers of the Pokémon series had in mind from the beginning, as the cover of the original pitch document for the first game (back when it was called Capsule Monsters) shows two different beta Pokémon that are moving in almost the exact same way as Gengar and Nidorino.
It's a shame that we didn't get a chance to see the iconic battle between Gengar and Nidorino displayed using the technology of the Nintendo Switch, but it seems that the developers felt it was more important to introduce the mascots before showing a battle, as the battling aspect of the game has been downplayed compared to earlier games in the series in favor of something that younger and more casual fans can appreciate.
It was still a nice touch for the developers to include a shoutout to the first battle of the series in the player's room.