Most stories have a beginning, middle, and end. Even a show about nothing has something zany and inane happen to our characters every episode, while getting some amount of resolution by the end. However, the same isn't necessarily true for a series as a whole. Some series are so homogeneous in plot you could air a season 1 and 5 episode side by side without telling the difference. Others have such intricate plots, you can tell which quarter of which season you're watching just by looking at the subtle nuances of the main couple's relationship.