This is a must have for any avid Steve Reich fan - if you thought you'd learnt a lot by listening to and watching lots of interviews, you don't know anything until you have read this book.
There are some really great score samples and really interesting opinions that you may have already known Reich holds, but expands on everything in great detail. It's interesting to learn about his musical history, and his writing about it just makes it all the more interesting. Some great diagrams too; one which stuck in my head is the orchestral layout diagram of The Desert Music - this immense, rich instrumentation actually has quite an interesting layout when performed.
If you want to learn even a little about Reich's work, get this book. It's precious.