User blog comment:Kaido King of the Beasts/The Potholes of One Piece/@comment-3351696-20140817031810

The biggest problem with fishman island was that Oda was unable, ... unable to introduce enough new plotdevices, characters, themes, etc without blatantly repeating himself. We already knew Jimbei, we already knew about Fishmen, Mermen, Arlong, we already knew a lot. With the massive suspense that followed from Water Seven when Kokoro first mentioned that the island was "coming up" and to the point where they actually reached the island, the massive hype couldn't match up to reality.

I do agree though, it was way too long and the Strawhats didn't gain much. No real powerful antagonists were met. It was sadly an inevitable drag.