I mean, the actual SAO part of SAO isn't terrible as far as haremshit power fantasies go. It actually could have been interesting if they just stayed in Aincrad for the entire series and it focused more on Kirito and Asuna developing as a couple, the complications of long-term life in an MMO, progress slowing down more and more as the enemies become more dangerous and intelligent, delving more into Yui and Cardinal. Give some Kayaba-centered material where he's reflecting on and reconsidering his motivations.
Basically leaven it with some .hack and maybe throw in a little Legendary Moonlight Sculptor for a conclusion when the survivors finally get out and have to recover from a multi-year coma trying to reintegrate into society.
That's kinda the thing, there's a lot of room to tell interesting stories about being stuck in MMOs, it's just that it's also a really easy shortcut for lazy self-insert trash. LMS, .hack, Log Horizon, Grimgar, Overlord-there's plenty of series that include elements that are genuinely fresh and fun, the trick is just in building one that avoids all of the bad shit and actually operates with an understanding of how MMOs and their players work/behave (which is one of the biggest failings of SAO).
Here's one half-assed idea I had for that sort of plot in a SF-fantasy setting: a research institute is preparing for an upcoming reality break that'll fuck with physical laws and introduce magical corruption into the world on a scale likely to disrupt modern civilization beyond repair. So they establish safe site facilities, fill them with semi-suspended animation equipment, and build up towards announcing a full-dive MMO upcoming, with a whitelisted beta test of, say, 50,000 people, and use that to recruit players.
It's advertised as a paid 1-week trial where applicants will be playtesting on-site with company devices prior to testing with more limited home devices, with players receiving financial compensation for their time. They get in, pods seal... and they are stuck in the "game" for however long it takes for the reality break to occur and largely stabilize. The game itself is a hardcore Souls-like with sharp caps on abilities which approximate peak human conditioning, substantial death penalties to discourage suicide-running, and high incentive for cooperative play; the VR pods allow for a degree of force-feedback and movement to enforce ongoing physical activity (to tone, avoid atrophy, build stamina, &c.) with individually regulated nutrient feeds and a slowed aging process.
Basically, the idea is to safekeep a sustainable population of relatively young people while maximizing their physical condition and experience, so that when they pop out they're primed to fight and survive with primitive tools in a hostile, magic-rich environment. Once that happens the story shifts gears into the characters dealing with the trauma of that big lie, associated issues, and the struggles of trying to rebuild civilization on a semi-deathworld. Thoughts?