This thread is stealing Stillakid's idea. <sorry>
What movie series have stood up well over their run? Which ones gave out during their run and when did it happen?
Having trouble thinking of the different series over the years? Here's a list to look over. To be honest, it never occured to me that there were this many.
Let's keep the discussion to those that have a 3 movie minimum to their credit to avoid a bulk of the movie series.