From UGO, Cameron on Salvation:

I think Sam [Worthington] is remarkable in the film because, well, I think Sam is remarkable in anything he does. Interestingly, I think McG did a good job in the sense…I think he was almost too referential to the mythos of the first and second film. He over-quoted them in a way? It didn’t feel to me to be enough of a reinvention. I mean the thing we did with the second film is that we reinvented the first film completely; spun it on its ass and made the Terminator the good guy, and came up with a whole new concept for a villain, it felt fresh. I didn’t feel the fourth picture was fresh enough. It also lacked a certain stamp of authenticity because Arnold wasn’t in it. I mean, he was in it briefly, digitally, but that’s not the same thing.

It’s very interesting that he didn’t feel it enough of a reinvention, and I know exactly why I feel that way.

It has something to do with John Connor and I’ll leave it at that.

Ross Out.