For me, the only misstep was the casting of Kyle Reese. In the original movie, he's a scrawny soldier covered in scars, bathed in PTSD. In this movie, he comes off like a dumb jock. Modern film casting focuses on herocis over realism, so I'll chalk it up to that.
Another thing in Salvation’s favour is that the late Anton Yelchin was absolutely perfectly believable as a younger version of Michael Biehn’s Reese; got his speech patterns down perfectly.