I guess I have changed in the last years and the authors I read have also changed. Sometimes the change is in the same direction. For example I still love nearly every book (old and new) by Nora Roberts. However when the change goes into different directions it's time to move on. I still can and will enjoy the older books by the three authors but that's it.
The reasons why I enjoy the books no longer are various. One author tends to create weak heroines (sometimes even pathetic) and heroes I don't like. Another uses plots that are not logical and characters that bore me. And the third writes the same story again and again plus I can't laugh about her jokes any longer.
Saying goodbye to these three authors is a bit sad but it also means that I have more time and money to discover new books and authors. So I guess it's also positive and exciting.
When is it time for you to stop reading an author whose books you enjoyed for years? Has it already happened to you?