I've had a chance to receive and read both the Annubis Murders by Gary Gygax and City of the Beast by Michael Moorcock.
Annubis Murders was far more lyrical than I would have expected. While the mystery revealed is somewhat unsatisfying [a la Sherlock Holmes the final reveal includes information not really available to the reader] it moved at a quick pace and was an enjoyable read.
City of the Beast is a romp on Mars in the style of Edgar Rice Burroughs. If you like John Carter, you'll undoubtedly like Michael Kane.
The thing that was most disappointing were the number of minor typos. ~5 in each book or so. Most were of a somewhat forgiveable nature (using the wrong real word in the sentence like form instead of from). A couple of the typos required me to think carefully about what was being said, but otherwise aren't too bad (though I certainly would like to see that changed).
I'd consider each of the books something that can be knocked off in short order. For Annubis Murders I read the entire thing between waiting for a flight and arriving at my destination, and City of the Beast was completed in a single work day between slow moments and breaks. On average, I think most people can knock one of these books out in about 8 hours of reading, they seem around 200 pages, and a fast reader can do it more quickly.
For that reason, if you're going to have a large amount of time to read, make sure to have two or three ready and lined up.
So far each book has also stood well on its own. While the characters are open-ended enough to allow sequels, (and perhaps prequels) there is no feeling that you're starting without enough information about the characters/events, etc.
I do recommend the subscription. I'm curious to see what else they've chosen for me when the next three arrive in the next day or so.