I think the main problem of WotC, and you feel it in every publication, is that they are trying to please a huge customer base that they don't really know that well. In the previous editions, when the game was much more confidential, it was a bit easier to create supplements, it was geek producing for geeks. But now that the game has exploded, I think that WotC don't even understand all the reasons for their success, and it's very hard to try and please everyone, especially if you don't know them that well.
As a consequence, the only adventures that people really praise are the low level ones, since there are fine for introduction for any group, and simple enough that mistakes are not made. CoS is a notable exception, but honestly I think it's just Ravenloft fans pushing it because I don't like Ravenloft and I find the whole adventure hanging on a paradigm that I can't work with, namely heroes supposedly being afraid all the time.
After that, the thing is that, if you read forums, there is a big push towards open-ended adventures, more sandboxy. Look at video games, most of them boast of a "vast, open world". And I think that this is what WotC has been trying to do in a number of publications, with more or less success, because it's damn hard to do and to describe. So much relies on the players and the DM, and in particular on the DM adjusting things to the path that the adventurers take, so that it's neither too easy or too hard.
For me, it's impossible to create a sandbox adventure that will work as written whatever path the adventurers take. I'm not saying that they did a poor job of it in RotFM, but I suspect that it's one of the reason for most of the negative comments. If you want to run a sandbox, you'd better be prepared to do a lot of work on top of what is written, it's as simple as that.
Moreover, it's a dangerous thing to do, because experienced players can become lost in a sandbox, and not enjoy the experience. The best known example is the sandbox part of SKT, we had a very experienced group who was suddenly lost and sort of ressented not at least having a few goals to chase. Same in my Avernus campaign, it took the very experienced group a while to understand that they could do whatever they wanted, could invent their own goals and ways to succeed. In the end, they are having a blast, directing whole armies in the blood war, but it took them a while.
So RotFM is just in the middle there, trying to please both sandbox lovers and people who would like more guidance, and sort of failing at both in the end. I think they should just accept that some modules should be designed with only part of their audience in mind rather than pleasing everyone, maybe with a few guiding scores on the cover like a 1-10 on a "linear / sandbox" scale, and warning that the more sandboxy, the more experience and work will be required from the DM...