Having previously read Greg Laurie's 'biography' of Steve McQueen, I expected many of the same shortcomings, and surprisingly, I found this one to be even poorer than the previous one.
1) All the filler material, personal and otherwise
Laurie is obsessed with comparison in his books, comparison that does not exist. He compares his own life to Johnny Cash's because they both took drugs and lost a close member of their family. If that is the benchmark for being similar to Cash, about half of the world's population can claim the same. Laurie comes off as a fan who is only too willing to dismiss the shortcomings of Cash, so this book comes off as more of a commentary on Cash's life than a biography.
Perhaps even more absurdly, there is often a callback to how similar Johnny Cash and Steve McQueen. This is not a comparison that most sane people would make, and it begs strongly that Laurie is trying to plug his other book. Again, he bases this comparison on the two having taken drugs and, get this, having been in the same town once. Incredible. I struggle to see the similarity he stresses, and the material would have been better left out, as it adds nothing to the plot.
2) The author's theological perspective
I find Laurie very difficult to take seriously, based on his theological point of view. He contradicts himself, by nature of his theology, and the book is really more of an indictment on his own religion than Johnny Cash's. He harps on about being a Christian being a decision that 'you have to make' and only 'you can do' and then says that only God can redeem. He refers again and again to Cash's backsliding, a continuous feature of his life, but never once considers that Cash might not have been a Christian during most of his life. Matthew 7 lays out a brilliant oration by Jesus that, in sum, says that you shall know if a man truly knows Christ as Lord by the fruit he bears, that a good man cannot produce bad works and an evil man cannot produce good works. Looking at a hefty portion of Cash's life, you can say that he bore bad works. Laurie forgoes the Gospel by suggesting that a man failing to love his wife and deep in drug addiction is a man redeemed.
3) The incoherent passage of time
This is perhaps a minor quibble, but I so often had to go back pages and pages to found out what year the events were set in, because Laurie bounces from the present to the past and future and back again. It doesn't make any sense to write this way, considering the biographical nature Laurie is meant to be pursuing, and it detracts from the book.
Overall, you are better off finding another biography of Cash rather than this one. Laurie even mentions some in this book, and I would have been better off reading one of those as well.