Most readers of Moby Dick seem to praise it for the wrong reasons and some miss the boat completely.
Criticize all you want of Melville's scientific inaccuracy, wandering themes, or even his improper punctuation. The guy wrote this thing in a year - not enough time to refine it, and it was a book he knew would not sell.
Underneath a mess of useless whaling information and Ishmael's rambling are ideas and questions that most people don't dare think about. Unlike Charles Darwin, Galileo or the fearless Ahab, Melville hid safely behind his metaphors and guided the careful readers to draw their own conclusions without completely leading the way.
Let me explain.
While to Ishmael, Moby Dick is nature's wonder and to Starbuck is just a whale, to Ahab Moby Dick is God, with his infinite power.
There are some disturbing things in the universe begging for an explaination, such as why one person is rewarded with happyness while another punished in suffering. There are feel-good answers, like the idea that the score will be evened in the afterlife and there are humble answers, like the book of Job, which suggests that man has no right to complain or question God. Melville's Ahab takes this to another level when he asks why man needs to be God's puppets. Ahab is insulted by God's creation of man, letting man live in suffering, "with half a heart and half a lung".
The bewildered God-fearing masses will not comprehend the depth Melville trys to take them. This most important theme was written for the pursuit of truth, not happyness. This book is not for everyone, and a lot of chapters are better off skipped, but those with enough empathy for Melville will find an emotional and intellectual adventure.