Real talk this new album is better than most of their pre-Watershed stuff. I do not understand the love for those albums, now granted I don't like much growling vocal stuff, but a lot of the old stuff doesn't flow as well as the new stuff and there's that old joke about them repeating every riff a dozen times. IMO Mikael's creativity has flourished since Watershed. A thousand other bands do what Oldpeth did, but there's nobody really doing what Opeth's doing right now, even if it is reminiscent of a period from decades ago, it still sounds different and fresh to my ears. The old stuff ain't going anywhere.
Ghost Reveries, MYAH, Still Life, Deliverance? I sleep.
Pale Communion, Sorceress, In Cauda Venenum? Yeah buddy.
See this is where I'm on the complete opposite of the spectrum. I think "Oldpeth" as you call them had a unique sound that no other band had and even bands that came close to filling some of the criteria failed to meet other parts of it. For example some other bands does the harsh/clean mix but might not be progressive (metalcore is a genre after all), there's some bands that fall in the "progressive metal" area that does both but you got bands like Dillinger Escape Plan that are more harsh vocals and short songs or a band like Between the Buried and Me that is much more towards the technical side and doesn't have the folk influence of the acoustic guitars like Opeth had. Or you have some other bands that go the folk route but don't do some other part of their sound. The classic Opeth sound for me was a beautiful mixture of harsh vocals, clean vocals, bone crushing heavy guitar riffs, beautiful acoustic passages and the balance was just so nice.
"Newpeth" does something I'm not a big fan of to begin with which is the 70s retro/old prog worship so even before I try to get into the music we're starting at a negative just because the band is doing something that I personally am not a huge fan of. 70s prog rock is cool but I'm not much for nostalgia worship, I feel like emulating what others have done before and more successful isn't the best route because I will usually just go for the originals then. And to me it's almost regressive in a way because Opeth used to be trailblazers of their own style but has in the last few years become more of a "homage" band. I don't dislike their new albums but I definitely feel something is missing. To me it's not as simple as the strawman argument people like to use that the naysayers of the new albums are just salty metalfans who are upset the band isn't growling anymore. To me like I said, their classic sound just had a great balance. Kinda like vanilla ice cream with chocolate sauce. You could separate the two and they would still taste good on their own, but combining the two just makes for something really great. I feel like listening to the clean Opeth albums (even Damnation, which I still think is better than the last few albums) is kinda like eating vanilla ice cream but without the chocolate sauce. It's still good but it could be even better.
As for the songwriting itself I think the strength of the newer albums is the atmosphere/overall mood of the albums which is usually really nice. Again, don't care much for the murky 70s retro sound BUT I can overlook that. Still when I think about the best non-growl Opeth songs I feel the best ones are still in the past. A Fair Judgement, Face of Melinda, Credecence, Harvest, To Bid You Farewell, Windowpane & Isolation Years are all some of my favorite Opeth songs and personally I feel few of the newer songs come close to that level. Opeth not doing growls doesn't have to be bad, I just wish more songs moved me like those I listed. Finally, last part of this wall of text I just want to say that when it comes down to it, I much rather prefer Opeth doing whatever they are passionate about (even if its not what im super passionate about) because if they forced a heavy album just because the fans wanted it then that would be even more disappointing to me.
(also only heard the new album once so far, sounded good!)