Novelist Jane Smiley suggests that length is an important quality of the novel .  However, novels can vary tremendously in length; Smiley lists novels as typically being between 100,000 and 175,000 words,  while National Novel Writing Month requires its novels to be at least 50,000 words. There are no firm rules: for example, the boundary between a novella and a novel is arbitrary and a literary work may be difficult to categorise.  But while the length of a novel is to a large extent up to its writer,  lengths may also vary by subgenre; many chapter books for children start at a length of about 16,000 words,  and a typical mystery novel might be in the 60,000 to 80,000 word range while a thriller could be well over 100,000 words. 
Interesting article, thanks Joe. Publisher’s requirements aside, I truly think the story will dictate the length. I write a mix of novellas and novels-my Chase Investigations private eye series are novellas, 15-25,000 words. My action/spy series The Division are 50-60,000.
Personally, I would rather read a shorter book that held me at every page, than drift through parts of a longer book. I find even some big name quality authors ave tended to fill out some of their bestsellers, which would have been fantastic shorter works.