4 stars for the three story arcs, 3 stars for the total package.
Piskor does a really good job condensing a HUGE amount of history into a coherent summary. This is no small feat, given how many retcons and time travel stories the X-Men have seen, and how many mutant books Marvel started to put out, especially during the Extinction Agenda years. This is definitely not a strict retelling of the X-Men's story; Piskor is definitely massaging some things to make the stories make more sense or to fit pieces together that weren't necessarily clear at the time (e.g. Mr. Sinister's motivations during the Mutant Massacre were never clearly explained at the time [and, indeed, his involvement wasn't even made clear until much later], but Piskor makes clear his involvement from the beginning and provides at least a modicum of motivation for the attack, which, to my mind, was never really done in the actual X-Men books). So, if you're looking for a 100% accurate history/biography of the X-Men, this isn't it. If you're looking for something that creates a coherent narrative of 30+ years of X-Men stories while smoothing over some of the weird gaps and lost threads, this will definitely do that for you.
As far as the book itself goes, like the rest of Marvel's omnibus releases, this is a hefty tome, but I find myself wondering if the content (and high price tag) is really justified. The three story arcs clock in at a mere 258 pages, then there are reprints of X-Men 1, Giant Size 1, and X-Men 268 (the Wolverine in WWII meeting Captain America issue) for another 89 pages, an additional 8 pages of Piskor's art, and the remainder is the "script" of the three arcs.
This is totally a personal preference, but I just don't find the inclusion of the script to be that compelling, nor do I think the inclusion of three already *heavily* reprinted issues is necessary. The art and photographs are more interesting inclusions, and I could see how including a couple of pages of the script (perhaps pages that show the differences from conception to execution?) would be nice, but cutting out the script and unnecessary reprints would have made this feel like a much better value. As it stands, nearly half the length of the book consists of already reprinted material or the script. For comparison, the hardcover of X-Tinction Agenda is 304 pages long, includes 12 pages of bonus material (pin-ups, promotional art, deleted scenes), and has an MSRP of half this volume. That kind of release would feel much more appropriate for the volume of real material, here, and would have felt like a much better value. As it is, it's hard for me to recommend this to people, because the extra material feels bloated and unnecessary. It doesn't feel like a hundred dollars of content, really.
Still, a fun read, and one I'd recommend fans of the X-Men check out, even if just for a reminder of how bonkers some of those early stories were. Plus, always nice to see Piskor's work, though I know his style isn't for everyone.