This is kind of trivial, but I like it when the main file is basically a flowchart of the program. So many people write this huge main functions. Or often the pattern happy smart ass fraction - even worse in most cases - this tiny ones. Which means I also like it when I can read the program like English, but I think more about reading function names. How people actually implement the functions, where they place the if-statement for example, is a matter of style and that can often be controlled with Perl::Critic. Structure is more important for maintainability, more precisely structure you can easily see and follow.