If you ask me, novels are not novels. The definition of the word takes different levels individually, as each person perceives a particular book in it's entirety.
Books which are supposed to be read at leisure, as some categorize it, cannot be differentiated into the 'serious' and 'non-serious' types. We are talking about fiction as fiction alone. Not dividing it into two different types. Somehow it does not make sense when somebody tells you 'Oh, you read the serious kind,'
Perhaps, one could say that fiction and non-fiction can be demarcated. Fiction is the imagination of the mind, let loose, influenced by real experiences which leads to the process of story-telling. Take any Dan Brown. Non-fiction also, sometimes, involves the same. But, i guess, it has a pattern followed by the author. And perhaps, specific examples which proves a point like any travelogue.
It's obvious that each one's likes are different. One may swear by Fredrick Forsyth, or Gabriel García Márquez for that matter. Observing the two names does imply differed opinions. To typify it, sounds absurd. One author may talk about the sexual relationship between a lawyer and his client, and the other about the strained existence of a mother and a son. It's simply the plot that varies, and the words, sentences used to describe, or frame the framework.
The views that we project on a particular book can also depend on the emotional quotient of the book, or perhaps the emotional state of our mind too. To generalize, perhaps, it's simply what one obtains from a book; a cold thrill, a laugh, or a sob.