This book is short, readable, interesting, truthful to Lacan, funny etc.
But if you want a serious introduction to Lacan which will lead you to understand sentences like "the subject is what a signifier represent for another signifier" or "desire is the desire of the Other" and other kind of Lacanian slogans, you have to know that THERE IS NO EASY WAY INTO LACAN.
I'm saying that because I started with Zizek's Looking Awry which is supposedly an introduction to Lacan as well, then I tried this one but, although you can get what Zizek is getting at, Lacan's thought remains in the background.
Although those books might give an exemple of what can be done with Lacanian theory, I really advice anyone to start with Bruce Fink's Clinical Introduction, and then to get to his Lacanian Subject. I really made a breakthrough in my understanding of Lacan with those two books (which are clear but demanding and rewarding). Another book you might want to consider is Reading Seminars I & II - an excellent collection of essays.
Zizek is perhaps one of the most witty thinkers at the moment, but you will get more out of him once you know more about Lacan, Hegel, Marx and Kant. When you have a good grasp of those thinkers, you'll see Zizek under a totally different light.
I also advice you to read Lacan's Seminar VII which is not really complicated if you have already some knowledge and that you take the time to read. Indeed, this seminar is the one from which Zizek seems to draw most of his material (about Sade, the sublime, the Real and the second death)