Contains the most comprehensive summary of lunar science in a single volume. It is essential for anyone interested in studying the Moon. I use it as a reference for basic lunar soil and rock properties, radiation flux, crater scaling relationships, and many other topics.
However, I would not recommend this book for someone interested in basic lunar knowledge, lunar observing, or amateur interest in human/robotic exploration of the Moon. It is usually too technical for these purposes, and it is probably not worth the cost and trouble of obtaining a copy. You might be happier with the cheaper and easier to read Lunar Base Handbook, which is still quite informative (you will find it references the Sourcebook just about every other page).
For an excellent and equally technical companion to the Sourcebook, I suggest the epic Geologic History of the Moon (USGS Professional Paper 1348).