The novel was originally envisioned as a two-part story; the first part covered the training of futuristic soldiers, and the second showed those soldiers in combat. Again, it seemed to play on my recent obsession with Full Metal Jacket, which has that same broad layout. To remedy this, I went back and expanded the plot to have five parts that followed the hero almost through the entire war in the future.
But last night, shortly after finishing the five-part version of the plot, I found this to be unsatisfying. Two of those extra parts seemed redundant - I had three large sections devoted to fighting when one was good enough - and there was a section that felt dedicated towards why the soldiers are fighting at all., which felt as much a hit on the head as the History and Moral Philosophy sections that Heinlein wrote in Starship Troopers. I'm not saying that it's not important for soldiers to know why they fight, even if it's on the basic level of survival, but I think this can be woven throughout the narrative rather than bunched up in one corner.
Ultimately, what I found unsatisfying about the five-part version was that I felt it sacrifice thematic material. The central theme of my novel is violence and finding a sense of identity through it. As a writer, getting through that is my top priority. I already know that I have to fight to get my reader's attention to begin with. If they see a book a thousand pages long, they might get turned off by it before they look at the first page. But if I can get my point across, tell a good story, and do it for several hundred fewer pages, then my chances of success have greatly improved.
If you have a story that spans a great length of time, focus first on your theme, whatever it may be, and don't be afraid to leapfrog over the other stuff if it serves no great purpose for your narrative. Saving Private Ryan was a great story, but the whole thing would have dragged on and on if we had to watch Tom Hanks and the rest of the cast going through Salerno or North Africa rather than jump to Normandy.