Wow -- I'm glad to see the 3rd party 4e market get off to such a sterling start! I've been playing D&D in various forms for almost 30 years and I've become pretty jaded about such things, especially after the glut of mediocre-to-useless stuff that flooded the d20 market not all that long ago.
This li'l pdf, on the other hand, is exactly the kind of thing that sets my brain on fire. Good production values. Cheap. Concise. It's well and cleverly written (kudos Fred and Lee), nicely illustrated (Storn!), makes good use of the 4e mechanics and brings a boatload of fun gaming ideas to the table. Races of the Shroud: The Apelord has really inspired me. Even if you don't feel the urge to explore the Lands of the Shroud setting, there's plenty of genuinely excellent ideas here to pirate.