These were surprisingly fun, in large part because of how familiar so many of them were, and that the editors seemed to do a pretty decent job of at least making an attempt to match the settings and characters in each entry with the artist most associated with them.
DC doesn't get a lot of the ideal candidates to draw these Earths. Alex Ross doesn't draw Earth-Kingdom Come, Dan Brereton doesn't draw Earth-Thrillkiller, Alcatena doesn't draw Earth-Detective Comics Annual #7, J.H. Williams III doesn't draw Earth-Justice Riders and so on, but there's a fair amount of very good art in this section, and flipping to and from the credits page at the back of the book is one of the many (many, many, many) pleasures the book offers.
The Earth I was probably most surprised to see was Earth-1:
The entry, illustrated by Batman: Earth One artist Gary Frank, explicitly notes that the various characters all exist in the same world (There's been no indication in the books published so far that this was the case, and all three seemed to stand alone and divorced form one another). Also of interest is the inclusion of Wonder Woman, in the text and in the illustration, as she hasn't been introduced yet. It was announced that Greg Rucka would be working on a Wonder Woman: Earth One book, and then it was announced that Morrison would be doing it instead, but the title of Morrison's original graphic novel about Wonder Woman has since changed its title, losing the "Earth One" sub-title and, one assumes, its designation within the line and, one also assumes, its setting on this Earth. But one shouldn't really assume anything, should one? I, for example, assumed those books were not set on a new Earth-1 (Is it of interest that the parallel worlds that the main DCU of Earth-0 have had the most interaction with so far have been Earth-2 and Earth-3, rather than their closest neighbor, Earth-1...?)