This is a very concise overview (as well as introduction) to DirectX. It doesn't only cover the latest version 11, but also compares the new features with previous version of DirectX too - which I find very useful as I have not been keeping up with the latest DirectX technologies for a while a reminder here and there comes in very handy.
It's not too big, it doesn't focus on the same component for too long (though, D3D is always the major topic in any such book), and the text is clear.
What I also like about the book is that the authors dive into the topic without too much extra history/story that we can find plenty of on the internet and/or other books.
If you are new to DirectX or haven't done it for a long time then this is the best [re]start.