Start with honesty: I don't know. Something in the character/plot/style mix, but setting, pacing, and vocabulary help, too. To misquote, I don't know what (the) art is, but I know it when I read it.
I started two books this morning (Don't ask; it's how I do things) and both sucked me in immediately. One isn't even a book yet; it's an unpublished MS that the author let go of with great reluctance over lunch the other day. She doesn't think it's ready; I can't believe I only got a hundred pages. I finished them before my oatmeal, now how am I supposed to wait to find out what happens while she burns weekends and evenings writing it down?
What's the pull? Good hook, great situation, engaging characters. But the whole is greater than the sum of its parts. The total effect is a step higher than the two books I started a week or so ago. Given a choice, I'd finish this story and leave the two published (and quite noted) authors face down on the night stand. I'll finish those books eventually, but they're reading material, not READING material.
The second book is *Murder Talks Turkey* by Deb Baker, the third of a series that I've thoroughly enjoyed. I looked forward to it, to reuniting with old friends, and the first chapter did not disappoint me. I anticipate my next chance to read it and again, those other two will just have to wait until Gertie Johnson's current adventure is over.
It may be partially mood; what I am looking for at a given time. Gertie's funny and humor is good, although I suppose a steady diet of zany would pall after while. But I've picked up lots of books labeled "zany" and thought "goofy" or "inane" or even "stupid." Whatever the page-turner is, it must be well done.
So there are books I read and books I can't wait to read. The latter are different because I think about them when I'm not holding on to them, wonder what will happen next, wonder how the author came up with the idea, wonder how it all comes together so nicely. It's not the same for everyone. Books I love get a ho-hum from others or even a "no thanks" after a couple of chapters. But a page-turner is a joy for a reader, at least until she reaches the end and then has to go out and search for another one.