This post will include my criteria of a good TV series. I have to point out that these are my opinions, therefore, some people (or you) might have different reasons on why they watch a particular show/s.
After watching a lot - i mean a lot - of shows over the years, I got fully aware on what constitutes a show which gives the viewers top quality TV experience. I became more critical and smart on the things I watch on TV.
For clarity, I'll rank them from the most important down to the least.
1. Character Development
A mean girl cannot be a mean girl from the beginning until the end. A killer cannot just be a plain killing machine all throughout. How the audience perceive a certain character must change or deepen as the series goes on. These are just some examples of good character development. Obviously, this is solely based on the writers of the show, because if not for them, well.. then there will be no show in the first place. What I look forward to is when characters are constantly faced with circumstances which change their personality: either for the better of for worse. As the show progresses, the audience must able to further understand the characters.