It's been many years since I read this work, and I'm ordering another copy (lost in a flood). Although the book would doubtless be helpful to those weathering seasons of doubt -- or worse -- its real value is probably for pastors, counselors, or mentors who encounter people with doubts.
Os has it that doubt and faith are not antithetical; that would be faith and unbelief. Doubt is faith in crisis perhaps, but not its absence.
I think the most valuable thing about this book is the way it treats various kinds of doubt. This taxonomy leaves the reader understanding the importance of avoiding pat answers to doubt as if all doubt shared some common basis and solution. It's SO not so. Until one recognizes what species one's dealing with, it'd be better to just shut up and gather more data, than to try the helpful mode and botch things completely with the doubter.
Personally, I'd say that doubt is a form of suffering. Just as one doesn't give cliche answers to one in grief, it's immature and useless to see the doubter as merely a problem to fix. This book is for the "adults in the room."
Finally, I well recall a judgment I made about this book the first time I finished its last page. "This should be considered the standard work on doubt -- but it's even more about faith." If your personal epistemology is getting stale, this volume will open the windows. :-)