I want to start by saying there are lot of valid reasons to dislike SAO. I enjoyed the Aincrad arc though it was flawed. I had a lot of problems with Alfheim and Gungale though there were also good moments. The two arcs that made up the second half of season 2 were great,, Mother's Rosario especially is my favorite so far. I haven't seen Ordinal Scale yet, I will be waiting for the Dubs to watch either it or season 3.
A common theme I've seen among critics of SAO, especially those who hate even the original arc, including Digibro himself in the PCP Podcast on "Plebs", is a notion that it was somehow supposed to be a Death Game Anime, and that the show then ruined it's own sense of urgencey.
Mirai Nikki was a Death Game anime, Fate/Stay Night and Fate/Zero are Death Game animes. Magical Girl Raising Project is a Death Game Anime (I just watched it and am still processing my thoughts on it). It's a genre that has an inherently limited appeal to me. I watches RP because I'm into Magical Girls, Mirai Nikki for the Yandere and Fate/ because I'm into Arthurian Legend and other mythologies. But if SAO had been structured like a Death Game that it'd have had almost none of what I like about it.
Digibro said in the last episode of the DigiBros Super Mario 64 let's play, when they were speculating on Zelda BotW (it was recorded before the game came out) that he doesn't like when Video Games have a sense of urgency. I agree with him on that, and that is why I like the very parts of SAO he considered the most useless. Every Video Game he could praise for not having a sense of urgency still has a theoretical sense of urgency, if Link doesn't get to the end and defeat Ganon eventually then Hyrule is doomed. And that is all the opening episodes of SAO were meant to do, establish a problem that they need to solve, eventually.
But the appeal to me was always about these character living in a digital fantasy world, not about them getting out of it. So my favorite episodes were largely the "Filler" which apparently came from the second Light Novel.
Digibro most hated the Murder Mystery two parter. I loved those, for the most part. As a fan of Holmesian stories I enjoyed seeing this speculation on how you'd apply Holmsian deductive reasoning in an MMO world. And when they figured out the deaths had been faked I was quite satisfied. Then the story dragged on adding some more twists and I soured on it a little.
I also agree that like in the original web novels Asuna should have killed that one guy. Asuna is also Best Girl.
Mother's Basement did a video on SAO where he said it was ruined by the Yui character turning out to be an AI, which he said destroyed the sense that anyone can die. I have come to be quite personally annoyed by shows wanting to create that illusion, and viewers who ever buy into it. If you're paying attention you can easily tell who isn't eligible to die on Game of Thrones, or the books it was based on. Ned Stark was a character created specifically to die early on creating that illusion, and Mami Tomoe was Ned Stark as a Magical Girl, in more ways then one.
And I'm annoyed by the people who want a show where anyone can die. Whenever I'm watching something and a character death happens that did not feel sufficiently built up to, it simply comes off as bad writing to me, even when it's a character I didn't much care for. This is part of what slowly soured me to The Vampire Diaries, a show I loved at first. And when it's done to a character I love, like my Waifu Anna, it just enrages me. I hate when shows do things just for shock value, and plenty of my favorite moments have been completely predictable ones. And that is Why I Like Prequels.
As a Christian I like Adoption themes in my fiction, something I talked about in a Force Awakens post last year "Rey is a Skywalker but not by Blood". So in this setting I quite like the idea of our protagonists adopting an AI character. So Mother's Basement desire to say Yui ruined SAO by being an AI offends me, just as it offends me when people say Dawn ruined Buffy.
That is all for this post. Expect maybe something in the future about SAO as a Gnostic Allegory, the first two arcs anyway.