O'Reilly already have Webmaster in a Nutshell and Web Design overlaps in coverage but the two titles are nonetheless complementary. Perhaps the forthcoming 2nd edition of Webmaster will sharpen the distinction. As it is Webmaster looks out from the server side, Web Design is more publisher/user presentation oriented - you probably won't need both.
Web standards change fast and some passages suggest the author was pushed to be both up to date (ie HTML 4) and in print - Some deprecated tags such as
are used in examples. Not, in my opinion, necessarily a bad thing; there are cases when style sheets are just too much overhead.
This book maintains O'Reilly's high reputation as the only computer books worth having. It does not condescend, it is not a bloated cookbook. It is a concise reference - and a useful revision tutorial - for people who know what they want to do, know it can be done, and just need to find out how.