What I consider milking is creating a too many games to sell to a audience. GTA isn't being milked, whereas AC and COD are being milked.
Now, how I came to this conclusion?
GTA has 7 main game ( not counting psp,CTW*,android,ios,and countless other ports I don't even know ) during it's 17 year. Each defined the series in its own own way. Sorry, i'm being a bit of a fan boy but prove me wrong if you think otherwise. So I think it's not being milked.
Whereas COD has 10 main games just under 14 years, not counting the handhelds and other ports and after modern warfare it has 7 main games within 6 years.
And Assassins creed has 8 main games(counting comet and unity, recently announced but not liberation) under 7 yrs. Though, I love this series, but 3 gave me a bad taste in my mouth so staying away for a while.
These are my opinions, on why GTA series is not being milked and the other two COD and AC are.
*(excellent game, bought a ds just for this game, totally worth it in my opinion)
Wow, I never thought mario was being milked, cause I love playing every new game that comes out. Though, I still don't consider it cause well, they innovate, they don't copy paste. I don't know much about MGS but the last one is just a cash grab. You didn't pay this much for Undead nightmare or Episodes from liberty city you still got more.
I don't think Watch dogs or Bioshock can be milked..
Mafia isn't how a franchise be. The second game sucked cause when you played the first game you had so much freedom with the map, you could drive for hours and still be not satisfied. Whereas the second installment was go to this point.. that point... cutscene.. bam bam.. this point.. that point. My opinion.
Btw, 1 question, of all the series mentioned in the op which one would you choose if you only could choose one for the rest of your life. You could only play new games of that franchise.