One of the things that every human being learns as they mature is that human relationships are an odd mixture of the simple and the complex. A mother is simply the person who gave birth to you. Simply? Oh my goodness no! A mother is the person who gets you going, but from whom you'll never get away, the person who gets you started, but with whom you'll never finish...
Art, too, is marked by such complexity. Kasimr Malevich's Black Square (1913) is just a painted black square, but it is also the focal point of a thousand years' worth of conversations about painting and representation, and the starting point for a thousand more conversations.
Melville's Moby-Dick, then, is just a great, big book about a whale. Or it is a kind of palimpsest of such complexity that we can and must write anything we like upon its canvas to help to explain it to ourselves. And very many of the differing literary critical strategies we might invoke will help us to explain different bits of its complexity: a Marxist reading that focusses on the experience of working on the Pequod and on slavery; a feminist reading that focusses on the lack of female characters; a religious reading alive to Melville's exquisite symbolism; a psychoanalytic reading that focusses on Ahab's mania... All can help, but none will finally pin Moby-Dick down. Indeed, the lack of success of any such critical strategies to say the final word on such a book is testimony to the wonderful ambiguity of Melville's art.
And how we feel about the book, its aesthetic effect upon us, can never be fully explained. We can use critical tools (formalist, narratological, structuralist, deconstructivist... whatever) to help us see how certain effects of the writing are achieved, but its overall aesthetic effect will remain beyond our ken (it is, in the end, an aesthetic effect on us, and we are forever just beyond our own ken). Art's effects are, finally, inexplicable. Like love, or family ties, there are explanations, but none that are fully complete.
In a post yesterday, Dan Green discusses the "descriptive mode of criticism" which he suggests is the best way "to carefully elucidate the manifest qualities of a given text." He quotes Rohan Maitzen who suggests that "one of the key features of this approach is working with a text on its own terms." Well, that is lit crit 101. If you are reading a comic novel and not laughing something isn't right; if you are reading a book called The History of Sport and it doesn't mention football, something may well be going wrong; if you are reading a book called The History of Cricket and football isn't mentioned, don't panic.
Every novel sets up an almost Platonic ideal of itself, and you can and should be able to measure it up against itself. That might be your first evaluative move. The question here being: what is the novel trying to do/say? It would be unfair to criticise it, at this point, for not doing something it never set out to do. (You might then judge one book against another -- not unlike how in a dog show a chihuahua can be judged against a dalmation -- by seeing how well it lives up to its own ideal of itself. If the vampire novel is scarier than the comic novel is funny and you have just one prize to give, the vampire novel gets it.) But evaluation is just one task. The next question might be, how well is it saying it? This has at least two parts to it. How well is it saying it on its own terms (if it is a dialect novel, its own terms are set differently to a novel in, for instance, Standard English) and how well is saying it per se (above and beyond the dialect, how good is this?)?
But, after this, we are left with at least one other question: was it worth saying? There is, then, an evaluation that needs to be made above and beyond the individual text itself. You can, of course, choose not to make this evaluation and stay with the difficult task of carefully elucidating "the manifest qualities of a given text", but the question of what literature is remains in the air. And that question can't be answered by e.g. a tenacious new critical focus. What literature is -- like what is a mother -- might be both very complex or very simple, but -- just like a mother -- it isn't something we can easily get away from. It may simply be an Ideal, but all is measured against that Ideal whether we like it or not.