Recently replayed and I still honestly think it's the best singleplayer campaign in any splatoon game. Splatoon 3's story mode is pretty good, a close secound, but it just doesn't compare to the sheer beauty of octo expansion's story. It added so much to the current knowledge of octarian society and really helped expand on Marina & Pearl's characters as well as expand on the story modes from Splatoon 1 and 2. And of course, the final boss is incredible and the boss theme is one of my favorites from the entire series. DEFINITELY worth a play if you're at all interested in splatoon.