I've finished watching the four seasons of Smallville that are available on DVD, and enjoyed them very much. The show does suffer, however, from "will-they-or-won't-they" syndrome. (Are Clark and Lana ever going to admit they love each other? And after four seasons of waffling, does the viewer really care?) Sexual tension is an important part of any show with a romantic component, but stretched out too long, it tends to become annoying, and the writers have to resort to increasingly silly contrivances to keep it going. On the flip side, most shows that let the main characters give in to their desires jump the shark pretty promptly, so dragged-out sexual tension seems to be a necessary evil of TV writing.
This is a problem with episodic television, and it's even worse with soap operas, which revolve around romance. I noticed this syndrome when I watched Guiding Light years ago. There were characters who had been married eight times or more. Why? Because happy endings are boring, that's why. Actually, the happy ending itself (on a soap opera, usually a big wedding) is a kind of catharsis, a prize for the viewer after enduring the trials of the relationship. But what comes afterwards is dull. In real life, it's what happens after the happy ending that's the best part. In television or romance novels, it's boring. Conflict is what makes a plot go, and when there's no conflict, there's no plot to speak of.
What's true for TV writing is also true for novel writing. I think this helps explain why I've never been interested in writing a series. Even a good writer can overuse sexual tension when it's strung across several books. I think we're all ready for Stephanie Plum to settle down, though we probably can't agree on whether she should choose Joe or Ranger. I don't mind writing a series like Kindred, where each book is going to feature a different hero and heroine. But a series of romance novels featuring the same hero and heroine over and over again? Nope... it takes a better writer than me to pull that off!