TL;DR at the end, for those of you who don't want to read a big review.
There was less fighting than the last movie, so for those who crave fight scenes, you're going to be a bit disappointed it's more dialogue-heavy than the last SAO movie.
It had a solid narrative, I actually liked the dialogue, it made sense and expanded on the development of how peoples' behavior and moral character evolve.
The biggest and most blatant problem that I just couldn't ignore was that Asuna and Kirito are a huge duo in this movie around Floor 5 (their characters are around lvl. 17). I can't stress this enough, like, they're almost always together. Because of this, it's obvious the movie totally strays from its source material (the original SAO anime itself), as in the original source material, Kirito is a total solo player until he meets Asuna later, when Asuna becomes 2nd in command of The Knights Of The Blood Oath (They're around lvl 50-60 at this point)... and even then, their relationship is a slow, gradual-developing partnership.
Asuna also acts like a completely different character. Asuna admits in the anime that until she met Kirito when Kirito was sleeping under a tree, she cried herself to sleep every day, experienced constant nightmares, and held a FIRM disdain for the game. In the movie, Kirito says multiple times that he and Asuna are "partners." It's totally ridiculous, because Kirito's hesitant to get close to Asuna even after first meeting her (they certainly weren't partners until the latter half of their relationship), and again, this is WAY LATER THAN FLOOR 5.
The animation itself was good, though not as good as the last one, but that hardly matters.
The characters being so different from how they should have been was a huge blow to the movie. This doesn't seem to be discussed by anyone else from what I've found from other reviews of this movie, surprisingly, so this could just be something that bothers only me, but I'm objectively right, nonetheless; I've rewatched this show like 4-5 times, so I know how the plot goes down.
Overall, it had some redeeming qualities, such as the good animation, good plot, and the fight scene that it the movie DID have was pretty darn good imo... but the state of the characters practically canceled it out. I would give this around 2.5 stars, but since that's not an option, I rounded down.
TLDR: Character portrayal in the movie is a disgrace to the anime, but has good plot, good dialogue, and badass boss-fight. Should be 2.5 stars, but google won't let me so I rounded down.