Most engaging novels for me always had dramatic turn of events and a twisted ending. I personally like the thriller genre and tend to read a lot of mystery, detective or horror because the suspense makes it so hard to put down. Also, like the response above mentioned, if I personally feel connected to the character then the story feels much more personal and keeps me engaged a lot better.
To me, the most important things to make me engaged in a novel are character development and relevance. If I feel a connection to the characters or, more importantly, am drawn into the role of a character it makes it hard to stop reading. Secondly, if the setting is relevant or a situation I can envision myself in it draws me into the world of that novel further. The books that I tend to have a hard time putting down are the ones where I relate to the character in a situation that is believeable to me.
For me, the answer even varies from book to book. Books like The Hunger Games series were read-in-one-sitting books for me because the plot was so entertaining (and fast-paced, full of action, etc.) but also because they are written so simply. These books, for a heavy reader, were quick reads. This is not to say every quick-read has been the same way. The Twilight books seemed to take a lifetime for me, and even then, I quit mid-way through book 3, due to boredom.
Of the novels that have captured me the same way, but weren't quick reads, it was more likely that they hit me in a time in my life when I had the time to devote to the reading, and also was connecting with the story or the characters.
There will not be one particular answer to this question. I think that there are a variety of reasons why a book is "so engaging." Certainly, the techniques that an author uses to engage the interest of the reader is a part of this process. The development of constant suspense is a part of this, for those who display a preference for this. I think that there is something engaging about characters and the characterizations that an author offers. Sometimes, the style of a writer in describing aspects of an environment or setting is powerful. Yet, one more reason could be the ideas that are being advocated and the development of these ideas in the course of a novel.
In Collins' Catching Fire, there are many reasons why this novel can be seen as engrossing. Being able to fully understand how Kat is going to navigate the dimensions of being true to her own sense of self and the pressure placed upon her by President Snow in terms of not being seen as a subversive is interesting. The collision between desire and duty and how an individual finds themselves in such a situation is a very unique and compelling situation. It is something that intrigues the reader and is something that makes for good reading, reason enough for the trilogy.
definitely the topic, the use of literary tools(for example:metaphors, similies, personification,ect.) also known as figurative language. and also another gripping, engaging tool is suspense-it rocks.hope that helps:)