I think you have to read the "squint inducing" comment in the context of the whole review, which finds nothing praiseworthy about the show. It's entirely within Green's prerogative to say that he didn't like the show, or that the show didn't meet his expectations. But as the other reviews demonstrate, there's something to like about the show. An honest critic should review all aspects of a show, both its brilliant moments and its blemishes.
I had to look hard to find anything remotely resembling praise in Green's review of KPOP. And really, found nothing. Even mildly positive comments are backhanded, in some way or another:
"Only among the members of F8 does the conflict feel fresh and worthy of exploration in song ... [t]he songs, unfortunately, do not take up the challenge of investigating that issue."
"[I]t's hard to say whether Brad's "Halfway" and MwE's "Mute Bird" -- acoustic songs simply staged and feelingly delivered -- are actually lovely or merely a relief."
Contrast Green's KPOP review to his review of other less-well-received shows.
Only Gold: "[I]t is so pretty to look at, and so musically dreamy. . . . [T]he shows, essentially dance revues, use the lyrics for mood and just a suggestion of plot."
Almost Famous: Praise for "Morocco," and Solea Pfeiffer's portrayal of Penny as "dreamy but slippery." Still, with this one, a lot of backhanded or conditional praise.
Funny Girl (original): Beanie Feldstein is "good. She's funny enough in places, and immensely likable always."
Paradise Square: The dancing explores, "far more subtly than the book, the place where appropriation and joyful sharing meet. . . . Kalukango . . . somehow alchemizes the remarkable difficulties of the role into her characterization, making it incredible in the good way instead of the bad."
The gist of Green's review is, "If you don't like K-Pop (the genre) and/or if you don't speak Korean, you won't really like this show." Which is quite unfair. I know folks who saw and liked the show, despite not liking K-Pop or speaking Korean. I speak Korean, but don't particularly like K-Pop; while there are moments that may resonate differently if you understand Korean, the thrust of the show can be well understood even if you don't speak a word of the language. Whatever you think of the book (and I agree that it's the weakest part of the show, though now serviceable unlike earlier iterations in previews), there's deliberateness in how the characters speak in Korean, so that the message is understood even by those who don't speak the language.
Quite frankly, while I could usually stomach Green's reviews (and agreed with many points therein), I stopped taking them seriously after his, "LOL &Juliet is fun!" review. That particular show, while very likeable, has quite a few warts -- warts that Green's review glosses over. ("I could have used a bit more brain, though," may apply not only to &Juliet, but perhaps his reviews as well.)