As a person who's deftly avoided nearly every single trailer and news pertaining to this game, going in completely blind, it may seem that I can't hold a complete opinion on it yet, because it'll leave the impression that I may be stating wrong facts. However, I'll give it a shot anyway.
Personally, I think that forking off the Let's Go sub-series is a pretty smart move on a lot of levels. It works as a really good entry point to the Pokemon series for those who got in through GO, with the overlap of mechanics, and also the fact that we're going back to the very first generation, so it makes sense that they can start where a lot of the long-running fans started, rather than just being thrown into this region with little rhyme or reason. The other thing is that this is their first time developing on the Switch, and we're still in Gen VII. This, in my opinion, should make this a stopgap game so they can get used to Switch development without the risk of them messing up the next generation, potentially letting them go all-out rather than just give us a "tech demo" not unlike XY.
However, I've been moseying around several message boards, and it seems as though Let's Go, despite being nearly two months to release, has already amassed a negative reputation. I can see where this is coming from, and while a prominent complaint is that it's just a dumbed down version of Pokemon, note that Final Fantasy Mystic Quest did the same with Final Fantasy, and it was critically received really well, so there's no telling of what's in hold. Maybe they could end up going down a really dark plot or tearjerker ending...who knows. What we do know is that there's no ranked, so the competitive scene may feel left out besides privately-sanctioned tournaments. However, I'm going to go into detail about the other - and main - prominent complaint - the GO mechanics...as it ties in with what was stated.
So the main complaint is that this game borrows too much from GO and pretty much feels like "Pokemon GO 2", and I'm going to try and justify why that's a thing. So Pokemon GO, that was a success largely because the Pokemon brand was carrying it along, but nobody realised just how massive it would get. It didn't just attract people who'd been around since the first few generations, it also attracted people who hadn't touched a Pokemon game before this generation. This means that GO was a lot of people's first Pokemon experience, and it's definitely not just restricted to smaller children who have never grown up with the series - I've seen and talked to older players who have never played a Pokemon game before GO came out, despite being around during the first generation. As a result, the overall idea that's being conveyed is "Hey, did you like GO? You're gonna love this game...it's similar to GO but adds a lot more to it!"
With this in mind, it may be a bit of a stretch to throw the GO players into a standard style Pokemon game, because the chances are, they probably won't get some parts, such as the type chart (hence they had to use descriptors about the effectiveness of moves in SM/USUM), so a stepping stone was necessary. This is why Let's Go allows you to transfer your GO mons and focuses on the aspect of "catching" rather than "battling" - these are terms that GO players are likely to be more familiar with and will understand. In keeping to this, I see this game being another killer app for the Switch like Breath of the Wild, as hopefully, GO players flock in droves to get this "GO-like game".
Here's hoping they don't dumb it down completely though...
