At first "Let God Change Your Life" can be a little confusing. Is it for Christians or for those who have yet to make a decision? The first few chapters deal with how you can get saved. The rest of the book is a call to radical Christian living.
My thought on this book is that it is for new Christians or for anyone seeking a deeper relationship with Jesus. Quite a large portion of the book is dedicated to discussions about discipleship.
The exposition on the Lord's Prayer is also excellent.
What this book seems to emphasize most is that sharing your faith with others will prevent you from becoming stagnant. There is also an explanation of justification and sanctification.
This book is also a call to Christians to present the gospel in a way that is easily understood. There is a a section on how to witness and how to present your own testimony.
I think a better title for this book would be: "How to Live the Christian Life." If you are looking for a book to give someone who is not yet a Christian I'd suggest:
Done.: What most religions don't tell you about the Bible
~The Rebecca Review