Xero was an SF fanzine published by Dick and Pat Lupoff that ran for 10 issues from 1960-63. I wish I'd been astute enough to subscribe to fanzines in those days. I'd have made the acquaintance of some wonderful folks like those who wrote for Xero, including Roger Ebert (known as Rog in those days), Ed Gorman, Harlan Ellison, Avram Davidson, James Blish, Lin Carter, Roy Thomas, Donald E. Westlake, and many others. But I didn't get into fandom until much, much later, so I missed out on considerable fun.
The Best of Xero is so good that it makes me wish the Lupoffs had just reprinted the entire run. There's a very funny Sax Rohmer parody by Lin Carter (and his book reviews are fun, too), a great article on comic books by Thomas, a review of Psycho (the movie, not the book) by Ellison, a parody of "My Last Duchess" by Ebert, and other wonderful stuff, far too much to mention.
Some of it I'd read before, including Westlake's notorious farewell to science fiction writing, but I hadn't read the responses to it, nor had I read Westlake's follow-up. All of it's just as interesting now as it must have been 45 years ago.
Roger Ebert's new introduction is great, but I've spoken often about my fondness for introductions.
All I can say is that if you have any interest in fandom and its history you should own this book. Unless, of course, you're lucky enough to own a complete run of Xero.