The book has some very good points and some stories about more recent revivals that few people may know ever happened.
So why only a neutral rating? Because Blackaby contradicts himself repeatedly in a key area, by making one statement, then giving examples which contradict it.
Throughout the book Blackaby states that "experience-centered revivals" (led by laypeople) are more prone to excess than "Word-centered revivals" (led by pastors). But repeatedly throughout the book he gives examples of where pastors actually quenched the work of the Spirit.
Example: page 206 he makes the statement above. Yet three pages earlier (203) Blackaby gives an account of where, after a sermon (given by his son Richard) where the Spirit was clearly working, when Richard turned the microphone over to the pastor, the pastor announced that there was an ice cream festival that night, closed the service in prayer, and the staff went over for food.