I read The Challenge of Missions by Oswald J. Smith while I was traveling to Busan from Seoul. It was a short book, and the book read like a series of speeches by Mr. Smith, rather than a series of writings by him, which made it easier for me to read through. So even I, a clumsiest/slowest reader could finish it within 3 hours of train trip. (It was the KTX, the fastest rail link available between Seoul and Busan. People told me the seat's not as comfortable as some other alternatives, but I was very pleased that it only took about 3 hours to travel from Seoul to Busan. I wouldn't trade an hour for a slightly more comfortable seat. Oops, sidetracking...)
Mark Brazee, who wrote the foreword for the book, rightly said, "don't simply read the words, but listen to the heart of the man" (italics his). Oswald J. Smith, the author is amazingly zealous for the Mission, especially for bringing the gospel to the unreached people groups. I do not wish to downplay the author's obvious zeal for mission; if only I could have 10% of his! However, I will think twice before recommending this book, for I believe this book contains quite a few theological (and/or the way he interprets some passages of the Bible) flaws which, if unchecked, could lead someone to complacent/lazy approach to the Bible, and that in turn can and will only lead to even more grim consequences.
If you wish to know more about the early 1900's world missions activities and the way they thought about missions, this book could give some ideas. If you wish to get infected by this great missionary mind, sure, read this book. However, if you wish to gain a solid foundation on the subject of mission, or want to learn how we should go about doing mission, this is not the book you should base and build your knowledge on the subject.
PS. I've also posted this review over at the Shelfari.