Sword Art Online was big in 2012-14, but then it went quiet for a while. In 2017, though, it had a movie (Ordinal Scale), before exploding back in 2018 with two separate TV series. Gun Gale Online is a twelve-episode spin-off, while Alicization ended up lasting two years and nearly 100 episodes.
Anyway, it's a show about MMORPG games, where lots of people all log into the same virtual world. Season 1 had everyone getting locked into the game, with hardware that would kill them for real if they died in the game. The show's virtual worlds usually involve magic and fantasy, but GGO (Gun Gale Online) was a player-vs-player game in the first half of Season 2.
This spin-off stars none of the main show's characters. No Kirito, Asuna, etc. (We don't even meet Sinon, the GGO player who teamed up with Kirito.) Instead, our heroine is Karen Kohiruimaki, a tall student with a complex about her height. As part of getting over it, she plays GGO as a tiny female gunslinger called LLENN who wears bright pink.
It's quite fun. The characters are entertaining and it's a light, breezy watch. It gets even breezier if you start fast-forwarding through all the gun battles. I should have thought of that earlier. This is a show written by a gun nut (Keiichi Sigsawa), who even writes himself into the show as an unnamed novelist who sponsors the game (and then gets mocked by the main characters). It thinks gun battles are cool. It loves firearms and is far more accurate and detailed about their use than almost any other show you're likely to see. You'll have lovingly presented gun battles... but it's a game. It doesn't matter. Then, later, even when it does matter, they're still just gun battle scenes.
I never cared about the outcome of a GGO tournament, or about the bullet-ridden action scenes. Obviously I'd stop and watch a scene where someone had an actual conversation, but you can skip through at least ep.1, the middle ten minutes of ep.5 and the majority of eps.8-12.
That said, though, it says a fair bit that I still enjoyed the series. LLENN is lovable, Pitohui is an entertaining psycho (in her jolly, chirpy way) and M is far funnier and weirder than he looks at first glance. I liked the schoolgirl club. I thoroughly enjoyed the real-world stuff in the second half of ep.12.
Is this better than Sword Art Online? Lots of fans say so. The pacing's better, it's far more knowledgeable about shooter games and the characters are more of a laugh. That includes the mind-bogglingly deranged ones, i.e. Pitohui. Personally, though, I can't heap too much praise on a show I kept fast-forwarding through. Gun battles. Characters getting excited about guns and calling them "beautiful". Bloodlust that's slightly disturbing, even in this video game context.
But I definitely enjoyed the show.