I read the previous review and couldn't agree less.
I'm a nonprogrammer who has tried and tried to learn Java (for about 4 years now, on and off). I've read Ivor Horton's book, Bruce Eckel's book and many others. I do not read the "for Dummies" books because they're way too cheesy and elementary.
Head First Java was such a breakthrough experience for me I don't know where to begin. Maybe I'm just exactly the kind of learner they were designing this book for, but I don't see myself as any different than anyone else. Not only did I finally understand concepts that were unclear to me, I also found myself doing each and every exercise willingly and immediately, something that didn't always happen with the dry exercises found in the other books.
Perhaps most importantly, these two authors deeply understand something that is so lost on other authors: how to prioritize the important information and leave the rest to appendices. After reading this book, I almost laugh at other books that go into deep discussions of bitwise operators near the beginning of their books.
Anyone who compares these books to the Dummies series isn't getting it. I found the exercises in this book easily as challenging as the 4 inch doorstop books. I thought the humor was fine, unlike the Dummies books and their unbearably lame jokes.
Too be honest, exactly why this book was such a breakthrough for me is a bit of a mystery even to me, because the authors use so many innovative learning techniques on every page.
I just hope O'Reilly takes a strategic approach to this series rather than a shotgun one. Rather than release a Head First book for ASP.Net and all the other hodgepodge technologies, I'd love to see Head First books that take people through the chronological skills needed to become great Java Developers: the Unified Process, Use Cases, UML, and Design Patterns, to name a few. They hava a lifelong loyal reader in me, and I hope they nurture that relationship rather than just "pee in the wind".