I'm at the exact half way point now too and it could be the coolest novel I've ever read.
The main narrative and oceanography, biology, histories on artistic depictions, sea accidents etc.; all the nonfiction exposition on whales is written in such an articulate and erudite yet profoundly warm, funny and human voice. I can't remember a better narrator. Not to mention Ishmael is just an incredibly loveable guy even besides his wonderful speech. The chapter after the first lowering when he comes back on board the Pequod after a night stranded in the ocean and he decides to write his will was very witty.
The nonfiction chapters serve to assure your logical mind that the whale of this book, for all its supernatural terror and strength, is a very real thing. My thoughts going into the book were "whales are big", now I'm partially convinced, a bit superstitious in the way of the Pequod's crew, that they're maybe even capable of being deities.
All this, to not even mention the crew, its captain, the points of the narrative, and so on.