The Syndrome

All things have a time and place and all film series have a limited life.
I am enjoying the Resident Evil series, despite my original thoughts about zombie films. 
However, and this is a big (!) however, I'm not looking forward to the later films-I may be proved wrong but I think the series had run its length after four films.
This has nothing to do with Alice and Jill not being in, Claire might prove to be a good role-I haven't had the chance to watch Extinction. 
 To explain my point, here are a set of examples:- Mad Max had three great films, as did Pirates of the Caribbean, but Police Academy went on far too long-the first two or three were good but after that it became same thing, different place. 
Directors and producers get fixed ideas on what they perceive the public want and in the end they trot the same thing out time and again, in the end diluting the series to "milk the cow."
At the beginning I said I wasn't looking forward to the later films, I hope I am proved wrong, but I have my doubts.