[DeepL Translation - needs review] This game is impossible to clear. No matter where or how you die, the only difference is whether you die early or ...... late. ......" It has been a month since the Death Game by Akihiko Kayaba began. The number of players sacrificed inside this extremely difficult VRMMO reached as many as 2,000. ≪The day of the "first layer floor boss attack meeting. On the day of the "First Level Floor Boss Strategy Meeting," Kirito, who has decided to only strengthen him...
Series: SAO Progressive is a floor by floor retelling of the Aincrad arc. It is essentially the story of Kirito and Asuna, and is generally 60% Kirito's perspective, and 40% Asuna's. It is often fun, light-hearted, and humourous, yet still serious (it's a death game after all). You get much a much more vibrant impression of Aincrad, what makes it so special, what's going on behind the scenes between players (with the ethical and ideological challenges that brings up) and the way they shape and adapt to the world there. The line between AI & humans is also a theme that features prominently in the series (just like later on in SAO), starting in book 2. Much more than just being just two OP characters, Kirito and Asuna are very integral in shaping how many significant events in Aincrad play out.
Book 1: This book covers Floors 1 & 2, and also includes a story about Argo (the infamous info dealer) & how she got her whiskers. It is by far the most interesting way to experience the Floor 1 story, as you get some very interesting behind the scenes stuff involving Kirito, Asuna, Argo, and some mystery players. (The anime adaptations left most of this out, sadly). You also get a more interestingly developed partnership between Kirito and Asuna. Floor 2 lets you watch more of Kirito and Asuna's progression, and involves some mystery solving, and an ethical conundrum. The interlude story with Argo is really enjoyable, one of my favorites! (It was also the first LN content I tried reading in Japanese!)
Overall the series has a lot to offer, and book 1 is only the tip of the iceberg there. The writing still suffers a bit from info dumps and unnecessary (re)summarizations, but that gets better as the game itself becomes more interesting. It's some of Reki Kawahara's best SAO writing (possibly second to the Unital Ring arc)
Language: it's generally a bit harder than the main series, but also feels more rewarding. You'll definitely need a lot of vocabulary under your belt for either series, and if SRS is your thing, jpdb.io has excellent decks for both series. It's a fantasy RPG, so you definitely get some occasional 役割後 (role speak - people imitating ninjas, samurais, etc), and a bit of kansai-ben. Argo can be a bit tricky to understand, given how much her expressions utilize katakana. But overall the characters are easy to understand, and very clearly distinguishable. You also get some interesting references to various historical or mythological figures (usually not Japanese ones).