Most of TV series made me sad because of... wasted time. Why so? I have impression of the following scheme happening too often. The series creators have the core plot in mind, however it isn't set in stone and can be manipulated on the fly to extend or shrink series duration. It seems like creators allocate a chunk of funds, shoot a season and look at how it was recepted. If season goes well, then another season comes next. If not, then plot suddenly wraps up and series end. In my opinion the best series I've ever seen were set in stone, as a whole piece of art, and done no matter what.