It's here! Actually it came in yesterday morning, but I was at work. This is a very initial impression. I plan to expound upon it, but for now, these are my thoughts.
First and foremost, this is v4 of the Reference Rules. I haven't noted any significant changes from the v3 rules. In point of fact, for anyone that pays any attention to this project, the changes have been available for some time. The project's author, Simon Bull, is very good about posting his ideas on his blog and on Delving Deeper's Google+ community.
I will say that I am undecided about the cover. It is a very nice piece, but I'm not sure it survived the reduction to booklet size very well. There are a lot of little details in the piece, and it is black and white. I'm absolutely certain that at a larger size, such as maybe 8.5x11, it would look fantastic. As it is, to me it looks good, but too dark and too "busy". I hate to be critical about a game I love so much, but that's my honest feeling about the cover.
Speaking of the cover, the stock seems a little "light". I routinely cover all my softback game books with clear shelf liner. I definitely recommend that here. It added just the right amount of weight to the cover.
I ordered this because I respect Simon's work on these rules, his respect for the original rules that his are derived from, and his scholarship in these matters. I have two sets of the v3 rules printed, and didn't intend to order anything until the Reliquary finally comes out. I felt like giving my feedback was the least I could do to support Simon's work, though. I'm very happy to order this, offer my thoughts, and get some of my houserules posted this weekend. We'll see how that part goes. I do have some ideas, but actually getting them typed up and posted. Well, therein lies the rub.