I think many people are intimidated by long books. What if I don't like it? I'll have wasted all that reading time! My brain will be full. I can't possibly read something else at the same time.
You see? Not a big deal. If big books intimidate you, my suggestion is to just hack at it 100 pages at a time. Then read a quickie. Then go back. Honestly, if you don't like a book by the time you've reached midway, your best off to skip to the end, and then quit.
<<At this stage of the game, I'm not picking up Book One of any series that already has double-digit installments published.>>
Actually, DO start such series. They have obviously garnered a happy group of readers. Most series pall after 8 or 9 books, so plan on the first 6 so that you can enjoy the best writing and then move on to another series or author. I'm a sci fi/fantasy fan and read a lot of series through, but the last series that I read that was still REALLY strong throughout was John Jakes (Kent family) and that was in the 80s under general fiction.