While Pokémon: Let's Go Pikachu! and Pokémon: Let's Go Eevee! are essentially just remakes of Pokémon Yellow, there are quite a few key differences. Namely, you no longer use Bill's PC to store Pokémon, and the way you catch Pokémon is entirely based on Pokémon Go. Granted, there are also some other changes, like the fact that you and your rival are not based on Red and Blue, though both of those characters exist. They're just older than you and already established in the world of Pokémon: Let's Go. There are other small changes and tweaks to the gameplay, but the core experience is nearly exactly the same. Just easier.
Since the Pokémon capture system in Let's Go is the same one used in Niantic's Pokémon Go, your Pokémon gain experience much faster when you simply catch a ton of Pokémon rather than by battling. And since you no longer battle wild Pokémon, it is much harder to grind levels using trainer battles. That shakeup is one of the primary reasons Let's Go feels so refreshing despite being a rework of a much older game.
The fact that it's damn adorable also helps.
As for the trainer battles you can take part in with either edition of Let's Go, even those are easier than they used to be. Type strengths and weaknesses are much, much more effective in Let's Go. You can now one-shot Brock's Onyx with a level 10 Oddish, should you choose. Misty presents a bit more of a challenge since Scald is a pretty brutal TM, however, if you picked up a Pikachu (either your starter or in Veridian Forest), and taught it Zippy Zap thanks to a helpful NPC in the Cerulean City Pokémon Center, you can get through that battle easily as well.
Also, because Let's Go is based on the Gen I games, fighting type moves are an absolute godsend against most other types. And your Pikachu will absolutely learn Double Kick early on–assuming it likes you, that is. Which basically means you're far too OP in this game.
However, because much less emphasis is placed on trainer battles, that feels a bit less like cheating than it should. The focus in Let's Go is less about getting badges and making it to the Elite Four and more about collecting one of every Pokémon available. Which really, is how the early games wanted things to go, but the execution wasn't quite there yet. Game Freak has obviously learned quite a bit since the days of Pokémon Red, Blue, and Yellow (or Green depending on your region).
Pokémon: Let's Go Pikachu! and Pokémon: Let's Go Eevee! also benefit from some later improvements brought in more recent generation games. Sure, the graphics are of a much higher quality, but you also get to do things like ride on your Pokémon as a way to get around faster. You also get to change outfits and dress your stater in matching outfits, which is stupidly cute.
Let's not ignore the "Play with your Pokémon" feature, which allows you to sit there and use your Switch's touch screen to pet your Pikachu or Eevee while they sit there and bask in your affection. And you can do that whenever you want. Endlessly.
Pokémon Go players can also transfer Pokémon from their mobile device to their Nintendo Switch to use in Let's Go, which is, frankly, adorable. Sadly, the switch doesn't work the other way around, so once you send a Pokémon to Let's Go, it's there to stay. Or get shunted off to the Professor and never heard from again.
Overall, the game's cute factor, portability, and novelty absolutely make it worth picking up. If it wasn't for the difficulty scaling, I'd absolutely give it a perfect 10.