Obviously that depends on the genre. I've found, though, that long, boring descriptions of the landscape, pages upon pages of history that are uninterrupted by action or character interactions or dialogue make for a REALLY boring book.
On the other hand, all of the books that keep me up until the wee hours of the morning all have one thing in common: on the next page, the world could end...and I MUST find out if it does! One of the books I'm reading right now has a lot of that "pages of history and description" stuff, but when the author manages to squeeze in some real suspense, I get this excited feeling in my gut that makes me keep reading. The unfortunate part is that that only lasts for a few pages, maybe a whole chapter, and then the book gets boring again.
In my WiP, I'm taking a page out of Jim Butcher's book (metaphorically since literally would be considered plagiarism). Each chapter must have conflict that is central to that particular chapter as well as the conflict of the overall story arc. With the smaller conflicts, I am doing my best to make sure that it's not resolved until the beginning of the next chapter, too. That way, every chapter ends on a cliffhanger, making the reader look ahead to the next page, and when more conflicts arise, they need to keep reading to make sure the world doesn't actually end.
So how about you? What makes a page-turner in your mind?