SAO was okay in the first season, even the second season, but then it became a bit like *The New Gate* (which I've read).
It seems novel but then if you've seen like dozens of books with a "virtual world" premise, "transported to another world" premise, or other such premise, then it looks a bit plain, especially when other titles have gone way past it to add their own flavors to the idea.
I think people underestimate just how many of these books there are.
Like The New Gate, SAO also plays the "invincible protagonist" role straight without trying to subvert it in some way (Overlord has someone who is powerful but also doesn't really know what he is doing). Or adding some sort of comedic element to it.
Kirito is kind of what you'd call a Mary Sue. He always wins. He even beat a programmer at a game which he created. All competent (he plugs himself into the computer system and effortlessly pulls down the fairy). Never psychologically vulnerable. A savior character.
I wouldn't really say it's bad but it is also frankly over-rated compared to what the show actually offers. Also, I think it's interesting to see new characters and new ideas, not seeing Kirito go off onto another map.
While No Game No Life also had characters who entered random games, and were immediately geniuses at it, the show was also pretty clearly a parody.
I won't say that every show has to be cerebral, that it has to be critically acclaimed, and serious in nature (that would be boring).
And honestly, if someone likes SAO, just as someone might like some of these Hollywood films, then that's cool. I think this sort of story has an appeal to a whole lot of people.
This is simply my experience with it.
Also, Kirito himself doesn't have that much of a personality / backstory. He's a fairly plain character. In other titles, the characters are fleshed out more.
That doesn't necessarily mean it isn't entertaining but when you have other titles which do try to put their own spin to it, and SAO is only offering another season of same old savior Kirito, then frankly, these are the ones which would be more interesting.