I've read maybe three or four really good books, besides the Bible, that have helped me in my walk with Christ. Tozer's "Pursuit of God", Lewis's "Mere Christianity", Bonhoeffers "Cost of Discipleship" and now Stott's "Basic Christianity".
I was hesitant to read this book at first, thinking it would be a re-hash of so many books I've read already on this topic. I was wrong. Stott has a very direct way of explaining his points and backs up each claim with scripture, which I believe is a bit different than C.S. Lewis's Mere Christianity. I felt myself reading a section and having to stop and process what he was saying for a few seconds as it really hit me. It's one of those books that you can feel Christ talking to you in the pages.
I would definitely not give this book to a non-believer, as I think it's more of a book for a person who's coming close to accepting Christ or who already has and is looking to strengthen his relationship. If someone doesn't believe, I don't think this is the book that's going to change their mind.