Chris Crawford on Interactive Storytelling is the second book my friend recommended to me on game design. Unlike A Theory of Fun, this one seemed a lot more technical and harder for me to get through. I am not a programmer and have never programmed anything, so the chapters on designing an interactive storytelling engine were especially tough for me to get through.
But with that disclaimer aside, Chris Crawford on Interactive Storytelling is a valuable book for game designers to read (and for game writers as well). Crawford details exactly what interactive storytelling is and how it is different from the stories present in games. He talks about the importance of verb thinking, how verb thinking is difficult for English-speakers, and how traditional games still give players the same few choices over and over. His book is difficult to wrap your head around in ways (especially if you are like me and lack certain frames of reference) but it is still worth reading.
About part way through, I came to the realization that I will benefit from rereading this book in the future. It's given me a lot to think about (and has made me want to try interactive storytelling), but I need to go off for a bit (and maybe learn some basics of scripting languages) before I come back to Crawford's theories.