The power of positive thinking and strong intentions is well-known and documented, and this short book does indeed offer some strategies for using these techniques. However, the book's primary focus is on establishing a relationship with Jesus Christ, and the author's attitude seems to be that the success of positive thinking hinges on that relationship.
I don't want to sound anti-Christian, but the powers of intention and the law of attraction are enough on their own to give all the results you could ever want or need. A belief in a specific deity or religion are completely unnecessary. Although Peale probably didn't know it at the time of original publication, the law of attraction is a scientific concept, not a religious one. Also, it's rather contradictory to tell someone that they have the power within to accomplish anything, but they need Jesus to do so. Either you have the power or you don't - Jesus has nothing to do with it. (And you DO have the power!)
If you are a Christian, I'm certain that the ideas in this book will resonate. And more power to you! But for those of us who are not, the book comes across as extremely preachy and outdated. There are many better choices on the same topic that don't have some mention of Jesus Christ on 90% of their pages.
(In the interest of full disclosure, I want to add that while I am not a Christian, I DO believe in God. I find it offensive, frankly, that people assume a belief in a deity means one is a Christian, and I want to make it clear that there are more options than just Christianity and atheism!)