Unfortunately, it is not actually going to be "free."
As Gaiman himself explains:
"The bad news is you don’t get to keep it forever. It’s yours for thirty days from download, and then the pdf file returns to its electrons. But if you’ve ever wondered about Neverwhere or wanted to read it for free, now is your chance. And free is free…"
No, Mr. Gaiman—in this case, "free" is most emphatically not free. "Free" is downloadable in an unrestricted format and yours to keep forever. Downloadable in a format only readable on full-sized computer screens and expiring after thirty days is nowhere near that. It may not cost financially, but the cost in annoyance at its restrictions is far too much to pay.
It seems decidedly odd that a writer of Mr. Gaiman’s clout would not be able to get his publisher to agree to less restrictive terms. It is all the more strange when you consider Gaiman will be hosting an Open Rights Group discussion in October called "Piracy vs. Obscurity," concerning "piracy from the perspective of a creator, what it means to be one of the tribe of readers, and why most people discover their favourite authors for free."
Neil Gaiman is one of the biggest names in fantasy today. Why is he not even able to get HarperCollins to agree to release one of his oldest works, which has long since passed its peak sell-through days, with no strings attached the way Baen, Cory Doctorow, Tor, Jeffrey A. Carver, and so many others have been?
Make no mistake, Neverwhere is a marvelous book. If this is your only opportunity to read it, then by all means you should do so—you will not actually be paying them for the privilege. But it is disappointing that this book which comes with so many aggravating restrictions has the indecency to try to pass itself off as "free."
For those looking for a real e-book of Neverwhere, it is available for $6.99 on Fictionwise ($5.94 with the paid Club discount) or eReader ($6.29 with the free newsletter discount). It still has DRM, of course, but it will at least be readable on hand-held devices and not expire after thirty days.