SAO goes back to its roots and slows the pace down for a more comfortable, immersive experience. Does still suffer from some SAO sins.
Sword Art Online: Ordinal Scale
While not without plot holes and a slapped-together ending, this grounds the series back down to its roots and keeps asking those very relevant questions.
Sword Art Online Alternative: Gun Gale Online
A great spin-off from SAOII, with a steady quality of episodes throughout.
Sword Art Online II (Season 2)
This season goes deeper into the psyche of the characters and explores the concept of Virtual Reality applications, ramifications, while also showing both the benefits and risks of immersing oneself online.
Sword Art Online (Season 1)
A fantastically immersive love-letter to MMORPGs backed with strong emotion that makes a great Gateway Anime. Then it goes sideways for the second arc before picking up the pieces for its second season.