I didn't like the writing style but the layout is excellent. The writing is patchy in the important introductory chapters and it seems unable to decide who the target audience are - sometimes novices, sometimes developers of JFace itself. Each chapter follows that irritatingly popular structure of preview, content, review that student psychologists are so fond of. When well executed, this structure can be effective in guiding students through a subject. Here it has been followed dogmatically. Despite this, the presentation of the content is incredibly clear and easy to follow or reference. The worked examples should be used as examples themselves in how to write programming books.
The content, with the sole exception of the chapter on events, is superb. The treatment of the text widgets in particular does a great job of getting the point across without swamping the reader in details. I think the depth is just about right. Anything not covered in the book can easily be looked up, but those parts that need explaining are covered. Events always seem to be the hardest part to explain.
I never intend to use SWT unless I get sucked into the IBM collective that is Eclipse, but I'm glad I read this book for an alternative view on GUI toolkits. I don't like how SWT is implemented and the use of yet another set of jargon is irresponsible. None of that reflects badly on this book though. Recommended even if you don't need it.