Well your favorite gals Leafa, Silica and Liz get the spotlight with Kirito/Asuna somewhat mysteriously absent. There's a quest, and they meet a Kirito look-alike who turns out to be a girl named Hiyori (opposite of SAOII?) who is also a SAO survivor. Their (Leafa/Silica/Liz) determination to help her overcome some of her own SAO trauma appears to be the heart of the story going forward.
It's nice to see these girls get some more characterization. Within the group, Leafa is the over-excited one, Liz is the joker, Silica is the kind but occasionally jealous one. Hiyori (aka Kuro/Lux) is a loner who plays to
strengthen herself and lessen her reliance on others (which apparently caused her friend's death in SAO). Of course she ends up joining the trio when they bail her out of a boss fight. This character development seemed rather premature in my opinion.
It does strike a lighter tone, not unlike the Caliber arc of SAO 2. They briefly discuss the crazy fact that they survived the horrors of SAO and still came back to play more games like it. This bit of retrospect is welcome and is something that the anime needed more of.
Overall, if you like the characters (minus Kirito) of SAO and don't mind some occasional fanservice, you should check this out. Just don't expect it to change your fundamental impressions of the franchise as a whole.