Salvation is actually my least favourite precisely because it came so close to being good that its failures frustrate me beyond the point I can get any enjoyment out of it.
For all the movie does well in terms of skipping the time travel and present day setting of the first 3 movies, it still doesn't quite distance itself or give itself whole heartedly to the heavy metal grimdark insanity the War Against the Machines should be, and that we saw in flashbacks (flashforwards) in 1 & 2.
John Connor is still not in charge, he's still just relying on warnings of the future and his mothers advice, the T800 is introduced as a big shock reveal, when we're all over familiar with it, especially the Arnie model, Kyle Reese is made too big of a fuss and focus on, tying us far too much to the first movie, the Cyborg stuff is dumb and ends on a ridiculous note, and it's all too optimistic and lacking the mechanical, emotionless cruelty such a world should be soaked in.
The only media I truly enjoyed since the second movie was The Sarah Connor Chronicles, since it was both doing something new, let us see how fucked up the future was and how brutal and callous both Skynet and the humans of that era were, and had a few scenes of John Connor being his own man and demonstrating what a ruthless motherfucker and tactical genius he ended up being, both utterly believed in by his army as the only salvation and hope of victory humanity had, and almost as alien and inhuman as the machines he fought, yet seemed to to have too more in common with than the people he led.