It proves that SAO is capable of mature storytelling when it moves away from video game gimmickry and focuses on the humanity (or artificiality) of its characters. Whether you are a die-hard fan or a lapsed viewer curious about how far the series has come, this is essential viewing.
War of the Underworld picks up immediately after. The “link” here is essential – you cannot watch WotU without Part 1. The emotional weight of Kirito’s collapse only works because we spent 24 episodes building Eugeo, the Taboo Index, and the cost of defying a godlike system. sword art online alicization war of underworld link