When an ordinary person turns 90, their family often puts together a photo collage, or sometimes a little desktop-published set of memories about fishing or the office. When the person turning 90 is Fred Pohl, the result includes a short story by Gene Wolfe and a poem by Neil Gaiman instead of a picture of the time they went to the Black Hills.
Or else--well, it's sort of a Blues Brothers/Blues Brothers 2000 feel to it. There's definitely a vibe of, "We're putting the band back together!" in this book, and everybody sort of plays their own thing and jams with the main attraction. There's a very brief tribute from David Marusek, and the Cory Doctorow novella that is in my opinion the highlight of the book. But other than that, the contributing authors are not only established in their careers, they're people who were established in their careers for Fred Pohl's 80th birthday and in many cases his 70th or even 60th birthday as well. What this means is that you can read down the table of contents and decide fairly readily whether this is the sort of thing you like: do you want short stories by Joe Haldeman, David Brin, Sheri Tepper, Brian Aldiss, Frank Robinson? You probably already know whether you do or not. My caveat there is that if you aren't in it for the Fred Pohl tributes--and, again, this is explicitly a Fred Pohl tribute volume, so not being in it for the Fred Pohl tributes is a little silly--you'll want to look at the ToC carefully to be sure of who has contributed an original story and who has contributed nonfiction reminisces about Fred.
You know what I wanted this to be, though? I wanted this to be different young (by which I mean "younger than Fred," so I'm not really being restrictive here) writers doing specifically Gateway-inspired stories as a tribute. I think they should do that for Fred's 100th. I think Emily Pohl-Weary should get browbeaten into editing it if at all possible, because I loved her sensibility in the Judith Merril bio. I would totally write a story for that so that it could get rejected in favor of stories by people much better than me. I think that would be awesome. Then someone else could read it and say, "You know what I wish this had been, though?" And then there'd be the idea for his 110th.