Extras include what I'm guessing is the Tales of the New Gods tpb, Walt's work on the New Gods vol 4/Jack Kirby's Fourth World series, numerous sketch/pencilled pages, and a cover Gallery of his New Gods vol 4/Fourth World stuff (he did all the covers for JKFW). All of the Orion covers are printed without dress and it makes them even better (though I do miss seeing "ORION RULES" on #8). The Tales of the New Gods backups have an unbelievable roster of talent on pencil: Walt, Frank Miller, Steve Ditko, Dave Gibbons, Jim Lee, Art Adams et. al. I'm not sure if it includes all of the backups, or simply reprints the Tales of the New Gods trade, but I don't believe anything's missing. It includes a Steve Ditko/Mark Millar backup I wasn't familiar with, but it didn't include Steve Lightle's unpublished backup. It does include Walt's New Gods Secret Files short story.
As for the main content, Orion #11 is my favorite single issue ever and the rest of the work is of that caliber (maybe the Wolfram arc suffers in comparison, I gotta re-read it). I flipped to my favorite moments from the series and it's absolutely wonderful seeing this in a larger format, in clean pages that aren't graying. Darkseid putting a gun to his head, the Death of Desaad (another instance where including the cover copy would wow new readers, as that was a huge bait and switch), the Sirius story, and the greatest sequence of pages I've ever seen in the tail end of issue #11. Everyone's probably seen the technicolor splash page but there are some monster pages that lead up to it. Simonson, Bob Wiacek, Sherilyn Van Valkenburgh, Tatjana Wood and John Workman all made one of the best looking books ever. Walt wrote one of the best comics ever.
One weird item: I was unable to find anywhere in the book the logo used for the Orion series. It wasn't a great logo or anything (not bad, though), just a little odd not seeing it. It was a classy move to put a huge reproduction of Walt's signature on the spine, maybe that's where the logo would've been otherwise.