I really love this book. I first read it in 1985, and reread it again for a meeting at the TCD Theological Society in about 1992. The story of Ahab and his monomaniacal mission infecting the crew and accelerating to the disastrous climax is a compelling one anyway; but Melville packs it with parentheses on whales and whaling, veering off occasionally into other topics such as the evil side of whiteness. As far as there is a popular consciousness about whaling at all, we owe it to Melville. Some of his statements have not stood the test of time, but all add to the picture, and the wordsmithing of the descriptive writing is just fantastic.
But I also love the way Melville plays with the narrative voice. My own feeling is that the first dozen or so chapters are written in a consciously moock-heroic voice, and that the book only gets serious once we reach the church in New Bedford. From then on, this is a grave tale. Melville switches from the first-person of the first part of the book, to various arrangements of omniscient narrator, tight-third with Ahab or the crew, or even dramatic dialogue and soliloquy, keeping us readers on our toes, challenging us to assess who is telling us the story and how and why.
Moby-dick is a very religious book, but not a very Christian one. The Bible is quoted freely, and as I said earlier the church in New Bedford is an early pivotal point. But Queequeg's worship of Yojo is in some ways better than, and certainly no more foolish than, the Christianity of most of Melville's characters and contemporary readership. Several of the other crew members are identified by religion - Fedallah, the Parsee; the sailor from Belfast whose one line makes it clear that he is a Catholic. This is, fundamentally, the story of a man who elevates an animal to become his god, and determines to slay it; and is of course in the end slain himself by the object of his obsession.
I tried Nathaniel Hawthorne's The Scarlet Letter a while back, and totally bounced off it, though the two authors were close friends and the two books published within a year of each other. Somehow Hawthorne's novel was both too verbose and too comfortable in its acceptance of the framework of Puritan social norms for me; Melville is also verbose, but not over the top, and the novel deeply subversive of religion and class (though not so much of race). And in the end, the prose is just fantastic, and you can't ask for more than that.
See also Ray Bradbury's Green Shadows, White Whale, about making the film with John Huston in Ireland.