Lucky Star and K-on for CGDCT
Evangelion for meta-commentary and deconstruction, to the point that future works that qualify often get called the “Evangelion of <genre>”
Fullmetal Alchemist Brotherhood and Attack on Titan for battle shounen
Bocchi the Rock for girls band anime, specifically
Lupin III: The Castle of Cagliostro for pretty much all of Ghibli
Akira for 90s anime
I’m aware that it wasn’t the first but there’s no denying that SAO kicked off a big trend.
Also .hack//SIGN was boring af; only part worthwhile was the soundtrack.