I'm not dismissing all critism of RPO, there are plenty of legit reasons to dislike the book or to (rightly) prefer Snow Crash or Neuromancer, but I'm not sure portraying the book as literary eyeball cancer in a sentence fragment reply is a criticism I shouldn't be skeptical of. I don't doubt criticism that involves the quality of writing or the those who don't like the 80's reference shtick, but some of the negativity seems unusually intense, and that's the part I question.
Ok, let's go over it a bit more concretely.
There are a number of different aspects of writing, and any given author will generally be good at some aspects and indifferent or weak at other aspects. Broadly you can divide these into two categories: the sorts of things commercially successful authors typically do well, and the sorts of things literary authors typically do well. Most of the former are going to fall under what I'd call "storytelling": fun characters, an interesting plot that's well-structured and has a few surprises, reeling in the reader over the course of the story and keeping them hooked. Most of the latter are going to be things like high quality prose, interesting themes, deep characters, etc.
To be a successful author, you want to lean on your strengths and shore up your weaknesses. If you're Brandon Sanderson you lean heavily on magic systems and on plotting and structure, because those are your strengths and can make up for the often weak characters and middling prose. If you're Steven Brust you lean heavily on dialogue and voice and maybe that helps you get by with a plot that's a touch thin. You still work on the things you're weaker at, try to get to a level where you're good enough so that they at least aren't detracting from your story, but you keep emphasizing those strengths, because those are what elevate your story. (This doesn't always work, and it doesn't always go unnoticed. Readers do criticize Sanderson's characters and Brust's plots, and so on.)
So what's the difference between the authors I mentioned above and Cline? Well, let's look at the weaknesses of Ready Player One. Paper-thin characters, a simplistic "evil corporation" plot that doesn't really go anywhere interesting, a standard near-future-with-VR setting that we've seen loads of iterations on since Neuromancer in the 80s. Dull dialogue, mediocre prose, a romance that relies on a tired trope. What does it lean on to make up for those weaknesses? Essentially two things: a decent amount of "page-turniness" and a shitload of 80s references that keeps the reader awash in nostalgia.
It's the latter that I think is causing the problem here (along with the sheer quantity of weak points). If an author leans on a skill to compensate for a weakness, that's one thing. If an author leans on something that feels to (some) readers like pandering... yeah, that's going to kick in a reflexive negative reaction for a lot of people. And indeed, you find a lot of people sneering about the 80s references and talking about how its just pandering nonsense.
RPO could've escaped this to some extent if the weaknesses had been fewer or less weak, or if there had been additional strengths in the writing that it could lean on, apart from the 80s references. There weren't, and it didn't.
Looking at the descriptions of the new book, it looks like more of the same: it's going to lean heavily on nostalgia. Will the writing be better? Maybe, I guess. But I'm not very hopeful. Barring Cline discovering a writing strength that he didn't know he had, I wouldn't anticipate any major changes in his writing.