I very much like long books but I'm OK with "medium" size books too.
I would probably pick longer books in preference to under 200 page books.
My current two favourite SF authors are Peter F. Hamilton and Neal Asher.
Asher writes "medium" length books but Hamilton goes for the epic size.
I have the "Night Dawn's" trilogy in hardbacks and those 3 books are really heavy (each is close to or over 1000 pages).
But I love those books! The story is so vast, there are so many "main" characters, it's great!
I have also read other long books, by other authors, which frankly bored me. I guess it's up to the writer to keep the reader turning the pages. Some can do it and some cannot.
This may sound weird but with a long book that I really like I start feeling a bit sad once I get to the last quarter or so.