This is the first book of the "O'Reilly Developer's Notebook" I read, and I must confess that I feel very confortable with this new concise and straight-to-the-point format. The book (170 pages length), written by the java best seller author Brett McLaughlin and David Flanagan, can be read in a weekend and has the great merit of being able to illustrate you all the new features introduced by Sun with JDK 1.5.
Some parts are really only introductions, because they try to cover huge subjects, like generics or the new java.util.concurrent package, but there are really a lot of informations, details and code snippets in this little book.
I particularly appreciated the fact that the author shows both pros and cons of new features, highlighting both what is good and what is odd or questionable in the new release of Java.
I think it is a good buy, especially for professionals who don't have the time to read thousands of pages but want to learn quickly what's new in Java 5.