Black Garterbelt points to a great piece by Gary Lutz in The Believer about beautiful sentences:

It took me almost another decade after graduate school to figure out what writing really is, or at least what it could be for me; and what prompted this second lesson in language was my discovery of certain remaindered books—mostly of fiction, most notably by Barry Hannah, and all of them, I later learned, edited by Gordon Lish—in which virtually every sentence had the force and feel of a climax, in which almost every sentence was a vivid extremity of language, an abruption, a definitive inquietude. These were books written by writers who recognized the sentence as the one true theater of endeavor, as the place where writing comes to a point and attains its ultimacy. As a reader, I finally knew what I wanted to read, and as someone now yearning to become a writer, I knew exactly what I wanted to try to write: narratives of steep verbal topography, narratives in which the sentence is a complete, portable solitude, a minute immediacy of consummated language—the sort of sentence that, even when liberated from its receiving context, impresses itself upon the eye and the ear as a totality, an omnitude, unto itself. I once later tried to define this kind of sentence as “an outcry combining the acoustical elegance of the aphorism with the force and utility of the load-bearing, tractional sentence of more or less conventional narrative.” The writers of such sentences became the writers I read and reread. I favored books that you could open to any page and find in every paragraph sentences that had been worked and reworked until their forms and contours and their organizations of sound had about them an air of having been foreordained—as if this combination of words could not be improved upon and had finished readying itself for infinity.

I really suggest you go read the whole thing. As a book critic, I can tell you that good sentences are alluring things that can often become traps. You can write a whole book review that has beautiful (or unbeautiful) sentences from a book and never once say anything about the book, or even about the author's writing ability. It's easy to pull sentences out and parade them around as objects of appeal or of derision, but you can easily get lost in the language that way. (B.R. Myer's Reader's Manifesto perfectly explains how many critics get lost in the hunt for good sentences and they never realize that the books they're promoting are crap. The Reader's Manifesto is a must-read for any serious reader, by the way. I can't read Annie Proulx anymore because of its vicious, hilarious and true takedown of her prose.

But sometimes you go so far in one direction that you forget why you're reacting in the first place. Lutz's piece is a brilliant appreciation, and defense, of why beautiful sentences matter.