I really, really want to use this in a campaign, which is the highest praise I can give any product (and is really the only thing that matters, right?). Many adventures and campaigns feature a sidebar or even a few pages about setting up a home base for the PCs -- this does the opposite, presenting the home base first, and then building adventure hooks and even campaign ideas around it.
The product describes the home base (the Sleeping Manor) and the surrounding area, but not in very much detail, which makes it easy for the DM to insert the Manor into any setting. Instead of detail, the focus is on how the PCs interact with the Manor -- what they can do there, what kinds of problems and benefits arise from Manor ownership, why they might want to improve the Manor, etc. This is the kind of stuff that drives game-play.
I especially appreciate how compact and efficient the rules are -- instead of dwelling on complex formulae and bookkeeping, you simply earn gold on a monthly basis, and pay gold to upgrade the Manor for various benefits. This allows the product to spend its space on what the upgrades are and what they do. Likewise, there are monthly random events that can happen (some good, some bad) and they are presented in a straightforward and rules-light manner.
I'm only giving 4 stars because, although I love the framework provided here, the specific HQ (a country manor with magic windows) isn't my first choice. I would LOVE to see a follow-up product with a few alternative home bases (an urban guild-hall, a keep on some borderlands, a large inn at a major trade crossroads, etc.), building off the material presented here.