I could say that this book is clever, revealing, stunning, but it's Lewis - his works are always really, really good and it's nothing new. The Screwtape Letters is a piece of art which is strong enough to touch and move everyone. There's something special in this book, but how should i call it? I think it's the simplicity and versatility...
I recommend this book to every Christian because it is one of my favorites. I believe that you'll spend a great time with those letters: filled with joy, laughter and reverie.