I'll differ with the brothers Gibbs to this extent. I think that Salvation is better than T2. I like Bale better. He is far more believable as a quasi military type, and his acting is just generally better.
The special effects were far superior and that is a huge advantage that newer films always have. But most importantly, this film fits. It manages to work as a future to the previous moves, while being a credible past to the infamous Reese. It does this without any noticeable retcon except what's necessary to fix the problems introduced through carelessness in T-3.
The "I'll be back" reference, was a bit of self congratulatory cheese that can be overlooked given the quality of the movie as a whole. I was surprised and gratified by the cameo appearance of my Governor (yes I voted for him) as the ineffable T-800M101 (geekdom beware my mad terminator skills). With no lines, this might be his second best role ever, the first being Kindergarten Cop.
My only issue is the striking resemblance between Sam Worthington and Brian Austin Green of The Sarah Connor Chronicles.