A new trailer has been revealed for Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee!, showcasing some new stuff.
With the trailer, we've received some information on how certain elements of the game work.
in the GO parks, the transferred Pokémon are actually shown interacting with each other. You can actually take Pokémon you transferred from GO into your adventure but you will need to catch them again in the GO Park first. There is also no limit to how many Pokémon GO accounts you can link to Let's Go - so you can Steal, Team Rocket Style transfer Pokémon friends and family caught into Let's Go! as well.
Once you transferred 25 Pokémon of the same species into the GO Park, you can play some kind of minigame in which you must collect and herd them into a goal area within three minutes while avoiding obstacle Pokémon. Succeed and earn candy (which unlike in GO, is stat-specific rather than species-specific) used to power up your Pokémon. You can earn candy by transferring Pokémon to Professor Oak as well, and by taking a Pokémon for a stroll using the shameless merchandising scheme Pokéball Plus Peripheral.
Alola Forms - confirmed to be in the game before - are obtained either by transfer through the GO Park, or by trading with NPCs ingame.
It is also confirmed, again, that Legendary Pokémon must be raid battled before you get a chance to catch them (except Mew, which you get through some Pokéball Plus chicanery buy all of our playsets and toys).
So. Some clarifications, though very little is new about this update. The Let's Go! spinoffs continue to be a Pokémon GO Simulator But In Kanto and definitely feel like they share more with their mobile cousin than with the main series, though in some elements they feature as more of an intermediate between the two. Assuming anything in Let's Go might carry over the the main series is probably silly - but it feels like it could make a good introduction to a (still simplified) Actual Pokémon Game experience for people who've played nothing but Go beforehand - and if anything, might be a useful testing ground for interactivity and a slightly more living world than we got so far.