Originally Posted by
LordJulius
This is basically DC's verson of the IDW Artist's Edition line. It contains high-resolution scans of the original art boards, i.e. the pencilled and inked pages, at their original size (which is considerably larger than what appears in the printed comics; in this case some of the art boards are 15"x20"). You can see pencil marks, whiteout, notes the artist or inker left in the margins etc and it is the next best thing to owning the original pages. The text is usually included, so you can read it as well.
The Sandman Gallery Edition has the complete art for Sandman #1 (minus several pages they couldn't locate but used other scans for), one page from every issue up to #75 and the complete art for P. Craig Russell's adaptation of Gaiman's Sandman short story "The Dream Hunters", with pencilled in text. Overall, it's 272 pages.
Oh, and while this GE obviously doesn't contain the whole Sandman series, there is already another one collecting all of Frank Miller's Ronin as well as one that collects several complete issues of Kelley Jones' Batman run. There will also be complete collections of the first League of Extraordinary Gentlemen series (vol. 1), The Killing Joke and Miller's Dark Knight Returns next year.