Normally I try to stear clear of such hefty books. I know, that sounds horrible but come on, if you can't tell a story in 200 pages or less, it means you are eityher trying to say too much or don't have anything to say and are just spinning out verbage (I'm looking at you, Stephen King!) If you're saying too much, pair down the focus and save the excess for another book. If you aren't saying anything, then go make Music Videos and stop killing trees.
The way I look at it, Fiction falls into two basic types: The Encyclopedic and the Evocative. The Encyclopedic books are just that; hugangous tomes over 400 pages long that give you the most miniscule details about the character's-- what brand of toothpaste they prefer and how when they were seven and they stole that apple from the neighbor's orchard and blah blah blah. Some people like this sort of minute detail. These people are anal retentive and need to seek profeshional help.
The Evocative books are the ones that read like poetry. They have a lightness of touch to them that is similar to Haiku; the author displays a comand of language that allows him to speak volumes with just a few carefully chosen descriptives. These are the books I am constantly seeking to bothg read and write and thankfully, their are a lot of them, mostly by modern authors: Herman Hesse, Ray Bradberry, Paul Auster, Neil Gaiman (for the most part).
I think a lot of this has to do with the fact that so many of the conventions of the novel are well known, so that author's can now feel free to use shorthand when dealing with them. 200 years ago, people neaded to have everything explained but now, we've become comfortable with mystery and ambiguity and can fill in the blanks left by the author.
Also I think the popularity of film has helped with this. People are now comfortable with montage and jump cutting so that author's can experiement with filmic techniques without feeling that they are betraying their craft or neccesarily speaking over the heads of their audience (Like a certain Mr. Joyce who liked to pepper his stories with Latin witicisms and Gaelic obscurities).
Or, maybe I'm just a child of the Media Age with a short attention span.