As a huge fan of the show, I originally bought this thinking only to plunder it for setting info and adventure ideas to use with a different system. Since then, I've become intrigued by the Cortex Plus system, and have been plotting to run it out of the book. In preparing to do so, I've come to find that the core rules, while solid, are often unclear, and perhaps not as complete as I would like, even as a fan of rules-light games. I eventually bought the Firefly RPG, which also runs on the Cortex Plus Action system, but a more, shall we say, evolved version of it, and plundered it for a few things, and now feel as though I have a solid set of rules under which to run Leverage.
Rules aside, the rest of the content of the book is fantastic. The random Job (i.e., adventure) generator is a thing of beauty, and all the Fixer (i.e., GM) advice is worth the price of the book alone. Even if you aren't interested in the Cortex Plus system, the vast majority of the book could still be of great use to you as you develop your own Leverage games using your favorite system (I could see it working very well with Savage Worlds, for example). I've seen some complaints that the episode guides at the end of the book are filler, but I prefer to think of them as adventure seeds and inspiration.
The whole book really comes off as a labor of love. If you're a fan of the show, you'll instantly recognize all the detail and references by writers who are clearly fellow fans. The PDF is fairly cheap too, so you're really getting your money's worth.
[4 of 5 Stars!]