It is a very subjective question. I generally like vibrancy; flow, movement. I have just finished editing a book which tells the story well, but is extremely detailed. Stays too long on the same subject, like some boring people we all know. Why describe a house in ten pages, no matter how detailed, when we can do so better in five?
So the ability to move on is tied up with flow, movement, vibrancy ...it must feel like a running river. Excellent grammar and short paragraphs as well as good sentence structure will hold my attention, including a great plot.
It must be gripping, not only in a dramatic sense, but with the ability to hold the readers attention and make him want more. A plot can be complex as long as it is well woven with twists and turns, balancing the despair with the joy, and summarising in a very clever way.
The start of the book should engage me straight away, and the genre should be something that appeals to me. For example, I used to be able to read most genres. X number of years later, I find that my Soul only wants to read spiritual books. Life changes us and also our focus or angle of vision. Much Love.