Both my wife and I are waiting for the final book of the Book of Dust trilogy, after really enjoying His Dark Materials and not hating the first two books (1, 2). So when we heard that Serpentine was released, we both got added to the public library wait list for an e-copy and waited for it. I got it first, but as she was out of town at the time I didn't catch up with her about it until later.
Let me just say that you can skip this "book". It's like 30 pages long and contains nothing of value for anything thing else, and really nothing happens. If you want to get it out of the library and read it, go ahead - but absolutely do not pay any money for this since it isn't worth anything.
I listened to the audiobook while I was going to sleep, and it basically put me to sleep but also was short enough that I finished it before I drifted off.
That's the best that I can come up with.
Everything else about this was dumb. It is so clearly an attempt at a cash-grab by Pullman that I've a bit disgusted. This should have never been published.
I've never given a 0 out of 5 as in my head it was a 1-5 scale - but this is absolutely a zero. Stay away!