I'm really surprised to see how the Terminator franchise continually gets trashed by different directors. James Cameron's original premise sets up one of the greatest movie villains of all time against a hero with one of the biggest challenges of all time, and never lets go of its audience, creating a suspenseful sci-fi/horror story that's really second to none. Yet after the first two films, it's gone downhill from there.
Undoubtedly the special effects are the star of this film, with flawless photorealistic CGI in the majority of shots. The industrial look of the machines is new and really helps to sell the concept that these things exist. At the end of the movie (SPOILERS), Arnold makes a reappearance as a T-800 looking the same age as he did in 1984, which was apparently achieved entirely through digital composition. It's as seamless as the photographic effect used in The Curious Case of Benjamin Button, and is the only point of the film where our audience applauded. Some of the other CGI suffered from speed/scale problems where machines seemed to move too fast to be real.
Terminator Salvation plot-wise is a mess, relying on a substantial knowledge of the previous films, and never really linking one sequence to the next. The main theme is that there's a 'kill switch' signal that can be broadcast to bring down the machines, while the appearance of a new character reveals a new prototype of machine that Skynet has built. And then there's about 120 minutes of non-stop action in between attempting to connect these two stories. There are huge leaps of logic too: the machines don't try to kill Marcus because he is a machine, but they tried to at the beginning before the audience knows that. Then in the final action sequence Arnold inexplicably disappears mid-sequence to allow John two minutes of expositionary dialog. During that period, I literally have no idea where he goes.
As for Arnold, they use every trick from the last films to finish him off, but apparently the T-800 is now impervious to molten lava, freezing and grenades. MAJOR SPOILER: in a clear indication of endless rewrites, the Terminator sticks a metal pole through John's chest (yes, actually *through* his chest) and in the next scene he is limping out of there awaiting a heart transplant like it's a flesh wound. At this point, we had officially lost cabin pressure on this film altogether.
The characters, for what they are, are one-dimensional at best, mostly existing to shout at each other or get killed. Even Bryce Dallas Howard's character (presumably John Connor's wife?) is never introduced or developed and seems to act only as a reflection to give John dialog. And actually, when they talk it's the only time in the whole film that people aren't yelling. Sam Worthington stole the show as Marcus, but even then it seemed his character arc was centered around "woe is me, I'm a machine".
Location-wise, we move from a gas station in the desert to submarines to helicopters to factories, without any sense of why we go from one place to the next. Even the idea of Skynet collecting humans in concentration camps is there for the imagery and little else (Skynet has become a chess player from the TV series onwards, whereas it was just a destroyer in Cameron's vision). And they now have robots that range from squid-like devices all the way up to 200-foot tall machines, which was more Transformers than Terminator, especially since they can contain motorbikes.
All I can say is that I'm really disappointed. This seems an easy franchise to extend for any skilled director, and fans have been wanting to see Future War since the inception of the series. This is the sort of film that Michael Bay or Jerry Bruckheimer produce: loud, confused, pointless and designed for the A.D.D. generation that just wants rapid bursts of endless action. T3 doesn't even look bad now, and the TV show is looking like Shakespeare compared to this.