After Johnny Mnemonic, I'm kinda shocked that he'd allow this. Granted film effects have come a long way, but it'll take a hell of a screen writer and director to bring that to the screen.
Edit: Guess the point is, even if it is really good, I'm not sure it could live up to expectations.
Oh, it's almost guaranteed not to. But who cares? Even if it's only half as good as the book, it'll be a great movie, particularly when you compare it to the bilge that permeates cinemas these days.
Gibson's writing is good because he develops incredibly complex social systems and structures for the reader to navigate. He does this mainly by leaving gaps in the world that the reader has to imagine or guess at. Some of them are filled in, as the plot progresses some of them are filled in and explained. This is incredibly difficult to do well in film. Directors are always tempted to show everything and producers demand it if there is the budget for it. The world becomes simpler, flatter, maybe a little silly.
Call me a lunatic, but I really enjoyed Johnny Mnemonic (the international version with the extra scenes from the extended Japanese version spliced in and sub'd). It was by no means a flawless movie (Keanu Reeves' acting was about as bad as bad Keanu Reeves acting can get, and they royally fucked up Molly Millions' character (apparently because they didn't have rights to use the actual Molly Millions character due to a Neuromancer movie attempt or somethig)), but all in all it really felt Gibson.
Stylistically, I think it was dead on.
EDIT: goes over the differences between the international version and the Japanese version: http://www.movie-censorship.com/report.php?ID=1523&In=Qu... basically, they removed nearly every supporting scene for the main Japanese character, and the explanation of the ending.
Edit: Guess the point is, even if it is really good, I'm not sure it could live up to expectations.