I notice that this book has received at least one negative review on Amazon.com. I guess this shows that the book isn't to everybody's tastes. Speaking for myself though, I have rarely been more impressed by a textbook.
I have had this book open on my desk for at least the last year, and over that time have been been repeatedly struck by how well organised the material is, and by the succinct and lucid way in which the author introduces the key concepts of signal detection theory. It is particularly good for users such as myself, who really only have school-level maths, but who aren't afraid of being led through passages of mathematical formulae.
This book is a superb complement to Macmillan & Creelman's (slightly more comprehensive) Detection Theory: A User's Guide, and I would highly recommend reading both together (probably starting with Wickens's book first). I would also particularly recommend this book to anybody who has been thrown in at the deep end of SDT and is struggling to get to grips with the fundamental concepts.
By far the best evidence of this book's quality is the ringing endorsement on the dust jacket by John Swets, one of the founders of the field. You can't really get better than that!