There are a great many problems with the three part sequel to the SAO Ordinal Scale movie.
The central one is the ill-conceived fusion of the sci-fi modern day plotline and Underworld’s essentially stand-alone fantasy plotline. The two never had any reason to mix. Assassin’s Creed does something similar, and the criticisms about the way that franchise mixes its past/present settings hold doubly true here since Underworld is effectively self-contained as opposed to being a reflection. The author could have easily wrote Alice and Eugeo’s story as its own thing with no association whatsoever to Kirito’s group and ended up with a far more consistent and immersive product.
Pretty much all of the remaining issues can be tied back to Kirito’s involvement with the story; spontaneous power-ups, random cameo appearances, last minute saves, questionable character motivation, harem elements, and bizarre plot twists all. Really, the only flaw that can truly be called its own is the re-occurring theme of using psychosexual megalomaniacs as main villains.
Vaguely related to all of that in a ‘you can probably watch this if you’re a fan of the genre’ sense are the series Runway de Warrette and Princess Connect! ReDive. The first of which is a fashion industry-focused Cinderella story overloaded with assholes who magically become nice while the latter is a conventional fantasy action-comedy whose protagonist has the personality of a particularly dull puppy.