Now, 90 days is a fairly short period of time to read through the Bible, which is why this book goes through several chapters (sometimes a whole book) in a day. What this means is that instead of a detailed verse by verse examination, the book looks at a more macro picture.
Each day goes through the chapters selected, interweaving the Biblical narrative with an ideas to consider. At the end of each day are questions for you to consider. While you could just read the devotional without reading the Bible (the entire narrative is told, after all), I think it will be much more enriching to read it concurrently.
Apart from going through the Chapter/Books, there are also two days dedicated to introducing the Old Testament and the New Testament. I foumd that this helped me in not feeling so overwhelmed, since it introduced key themes.
I want to end by quoting this passage on James (Day 82):
"The practice of faith affects our actions, our mouths, and our relationships. It's a deadly delusion to think that hearing and agreeing with God's Word is the same as doing it. A thousand messaegs from gifted teachers do no good if the truths learned from them don't produce change in our lives."
So yes, I highly recommend this book, but bear in mind, that just reading the book won't be enough. Put into practice what you've learnt.
Disclaimer: I got a free copy of this book coutesy of Tyndale Blog Network in exchange for a free and honest review.