Edit: I'm sorry for the lack of tl; dr. There's a general drop off of quality, weird social media garbage, a lot of systemic problems, etc. What I'm trying to say here is hard to summarize
Aside from the fact that it's mass produced garbage, I can actually say that I'm old enough to have experienced a period of anime where the production values, writing, and dialogue weren't exactly terrible.
I think a good example of my gripe with anime today is watching something like Fate Zero and then following that up with Heaven's Feel. The distinct drop in quality between those 2 adaptations is pretty stark.
The original Yu-Gi-Oh anime was absolutely wild. It's dumb in a uniquely entertaining fashion. There were so many sequels that were produced for Yu-Gi-Oh and every single one of them was completely terrible.
Watching Tenchi Muyo's OVA part 1 and part 2 was fairly enjoyable. Part 3 is so much worse for seemingly no good reason.
The third Tenchi Muyo film was abjectly terrible. It's quite possibly one of the worst films that has ever been made.
FLCL season 1 was legendary. Season 2 and 3 were substantially worse.
The new Evangelion films weren't exactly great.
Even as far back as Pokemon season 1, that season was pretty okay. Almost everything past the first 2 seasons were.... really bad....
There have been some bad adaptions for Berserk that have been mentioned from time to time.
Dragonball Super is weird. Nobody really seems to like Super. Even people who watch Super regularly treat it as some kind of Frankenstein monster.
Gundam has been pretty consistently not good for well over a decade. Gundam Wing was pretty insane. It started off with some super questionable writing and poor voice acting, and then it ended off being probably the best thing Gundam has ever been. And everything that followed was.... not very good...
Naruto was followed by Boruto. It's pretty bad. A large chunk of the 2nd half of Naruto was just not good.
I've seen people defend Hunter X Hunter's Chimera Ant arc so brazenly. And still, it's genuinely not good. Which is amazing, because almost everything prior to that arc was crazy good.
To be fair, a lot of these problems stem from the fact that the work being adapted is also consistently worse. It's not just anime. A lot of this coincides with the same drop in quality in the manga industry as well.
The nearly universal drop in quality across the anime and manga industries has been... frustrating...
Even more frustrating is the overwhelming number of fake reviews, shilling, bot spam, etc that are meant to hide negative reviews about anime and pretty much anything involving Japanese media.
The amount of weird shit that gets posted to review sites and social media in order to hide the general negativity towards the anime industry is just gross and weird.
Another poster, Ace T'Ken, brought up a lot of specifics about the problems with anime in general. It's a pretty good write-up, imo.
My take is, I think that these problems are more "noticeable" in modern anime. But, almost all anime have these kinds of problems to one degree or another, new and old.
It's pretty systemic. I still think that these issues became a lot more noticeable coinciding with a general drop in quality across the whole industry.
I would like to say, it's not like I dislike anime "inherently". But, there's just so much bad anime.
