In my opinion, one of the reasons for the gazzilion 1 star reviews is fear of change...
At the moment Gutenberg is barely usable, this is a fact, but that could be said of almost any software during production..

One of my clients has a vip pr company in asia they copy and paste a ton of press releases in TinyMCE, I talked to her about Gutenberg and I told her that soon enough it will be the new editor on her website. She did some googling, out of curiosity, and saw all the crappy reviews. She asked me to try it.
After 10 minutes of trying the thing she said something like:
"The problem here is that you present it to me as an editor if you tell me is an editor i expect to be able to use it like Word. This is much more, is a Canvas. And I think it has great potential once they get it to work."
She also said that the text block should be called "paragraph" because "that's what it actually is" and other things and I think she's kind of right on both the points.

I played a little with the blocks api and i managed to make a few cool looking blocks it's really not that hard considering that I almost don't know how to spell React... much less code in it.

Devs will make all sorts of acrobatics with blocks once they get the grasp on the basics and the metaboxes will keep working as they are today this has been made clear on the various github issues.

Widgets will be ported into blocks? What's the problem? There is a widgets api now there will be a widgets api then.

Maybe one thing i find annoying is that blocks are a little bit too atomic for my taste and that some things like social media buttons and author boxes i don't think should be part of an editor of any sort... but hey.. one less bit of code to maintain in themes and plugins..

Gutenberg is new and kind of clumsy at the moment but if one day we wish to have front end editing in core TinyMCE as we know it today needs to go..

Just my 2 cents..