You may have heard the story of author J.R.R. Tolkien who wrote The Lord of the Rings as one book before his publisher looked at him from across the desk and said “I’m sorry, John. This book is just too long. Break it up, will you?”
I am not saying that a massive tome will not be successful, because we have J.K. Rowling, Stephen King and others who write massive books whose thousand page beasts are climbing to the top of the New York Times best seller lists. However, some of the best literature in history has been less than 200 pages, and as an English teacher I have said many times to many students that less is more.
I am still pounding away at my post-apocalypse novel, but I’m seven chapters in and have only touched maybe 20% of the outline. I have found that I usually create such detailed and intricately woven worlds only to find myself wondering if I should write three books instead of only one. Here are a few considerations:
1. Word Count Blues – Most publishers are turned off by anything over 80,000 words. In this day of economic woes, nobody wants to publish that massive beast of a novel if it is so thick they have to haul it with a forklift. Yeah, Stephen King’s Under the Dome is 336,114 words in length but he’s Stephen King and you are not. First time publishes are much shorter. They can afford to publish King’s book because they know it will sell.
2. Breaking Up Is Hard To Do – Have you ever considered breaking the book up into smaller novels as part of a series. These are very attractive to people because readers have something to look forward to in the future from you. Maybe your only creative effort is this one novel. Nobody wants to be a one-hit-wonder. If you are starving for more ideas or more worlds to create after you finish your epic saga, consider breaking it up. More books means more chances to hook the readers.
3. T-i-i-me … Is On Your Side… Yes It Is – If you break it up, you will get the novel into the hands of your readers much faster than you would if you spent the year it would take to turn out a novel that big. This will give you more time for editing, backstories, character development, and all of the other things that make your stories sing.
4. At a Leisurely Pace – Let’s face it. A great majority of readers read at their own pace, usually when they get time in their busy schedules. Even though e-readers are supposed to speed us up, a study completed by Jakob Nielson in the summer 0f 2010 found that:
Compared with print, iPad readers were 6.2% slower and Kindle readers were 10.7% slower, though the difference between the iPad and Kindle results wasn’t statistically significant. Mr. Nielsen suspects the slowdown is caused by the screen technology in the devices, which is still less sharp than print. (Found under the heading “The Pace of Reading”)
So people who read using e-readers actually read slower than they read print books. Imagine how long it would take them to finish your book. Let’s hope you spin a good yarn and can keep them interested with your fantastic prose.
5. Quality Over Quantity – If your novel is shorter it will be easier for you to do the necessary editing that will be required to produce a more polished product. Grant it, you may be one of these people who is either independently wealthy or you are able to stay home all day and do nothing but write. Actually, you are probably like me and have a day job and kids and a wife/husband/significant other and you don’t have all that time. You want to produce a novel every six months or so to keep people interested and you want to produce quality stuff so your readership doesn’t dwindle. If you do break it up, make sure that you follow through and finish it before the flame dies. I made that mistake with my first novel (which I plan to come back and write the sequels for some day) but right now I’m focused on this project. I have a deadline I have set for myself, I will follow through on that, and I have built in time for editing, proofing, test readers, etc. If you do this, you may have more long term success.
Writing Is Hard Work 
You raise some really good points here. When I was getting started in writing, I worked under the illusion that longer meant better. I’d look at books like Thomas Pynchon’s Gravity’s Rainbow and Don DeLillo’s Underworld and think, mistakenly, that writing a long book would endear me to the literary world. But the problem with that outlook was twofold. First, I lacked the stamina and attention span necessary to keep working on a really long novel. Second, as you point out, publishers don’t want long novels, especially from unknown writers. In fact, when my first novel was accepted by the Permanent Press, the acceptance came with a condition: I had to cut about 100 pages from the manuscript. (100 pages!) I made the cuts, and I think the novel is better for it. And my follow-up novel weighed in at a very manageable 176 pages.