Although we finally get to see the grown-up soldier John Connor, played by Christian Bale, Terminator Salvation is not about John Connor, nor has the series ever been. He is the protagonist, but it is the terminators themselves, both playing the heroes and villains, that dominate the screen. In the fourth installment, we stick to roughly the same formula that has emerged since the second film -- both good and bad machines. One to hunt Connor, one to rescue him. The window dressing has changed, and the movie has moved solidly into an apocalyptic future, but the theme remains the same.
The compelling actor Sam Worthington plays the good terminator (you aren't going to improve over Kristanna Loken), a person who has been willinging (and unwillingly) transformed into a kind of hybrid human/terminator. Why? That's the question that Connor tries to answer while compromising to help save his future father, Kyle Reese, using the hybrid's help. Formulaic, fun, and just what you expect. If you are surprised by any of the revelations, or how the film ends, you really haven't watched this series very closely.