Update 6/8/09: Just read some background info on the film, and apparently that open-ended finale was the work of the film's director, MCG, who is some guy better known for directing music videos (like anyone watches those anymore).
Of course I didn't know about the total bait-and-switch unsatisfying ending until, well, the end. But that's far from the only thing wrong with this movie - or at least not as advertised. Did you think Christian Bale was the star? WRONG! Terminator/Cyborg Marcus Wright (Sam Worthington) is the actual star of this movie. He gets all the really good action scenes, and he's actually the hero who saves people (including John Connor). Where's Christian Bale? At home, washing his tights! Oh, no, wait this isn't a Batman movie is it? Well, you'd never know it by watching Bale - he delivers us a John Conn0r a-la-Batman. Seriously, his performance for both characters is the SAME. As for where he is? Back in the bunker, talkin' on his radio - while "Marcus" is saving Kyle Reese (Anton Yelchin), who if you've followed Terminator at all is actually John Connor's father - but in 2018 he's only a punk-ass kid who fashions himself as the Los Angeles resistance.
Which brings me to some of the glaring WTF's in this film. Some of this would be the SPOILER fodder, so if you still plan on seeing this turkey stop reading now.
Correct me if I'm wrong, and I know I'm not because it says so in the opening titles, SkyNet tried to wipe out humanity in a nuclear holocaust. But there doesn't appear to be ANY radiation. None. What isn't in short supply in this post-apocalyptic future, though, are hair products and teeth whiteners. These people should be glowing green in the dark, they should have radiation sores, tufts of hair falling out, teeth falling out - but from the looks of a lot of the ruins and cars SkyNet must have used "Lite" nukes - so weak they couldn't even burn the paint off of most cars near ground zero. But it was those bright white smiles that particularly cheesed me off. Then there's the big question of why on Earth the T-600 Terminators are so often wearing rags of clothing? These are the big, chrome guys. Ok, maybe they put the clothing on to cover up the chrome. But, wait, why is SkyNet chrome plating them in the first place?
Since the story takes place in 2018, SkyNet is still doing R&D on the T-800 "Arnold" Terminators. However, Arnold Schwarzenegger declined to appear in it, so I initially thought that's why they were fighting T-600's through most of the movie. But near the end a T-800 does show up to kick John Connor's ass. They texture mapped Arnold's face onto somebody else - at least up to the point where it get's all the skin blown off. Actually this installment of the Terminator franchise relies heavily on CGI for the terminators, which makes them a little less convincing on screen than in the previous movies - where the limitations of CGI at the time forced them to use a lot more animatronics and props, which interact with the actors far more convincingly. Lastly, back in a Resistance medical tent, John Connor's injuries from the fight with the T-800 send him into heart failure - he needs a heart transplant to survive. The cyborg Marcus says "Take mine." Gee, that's convenient isn't it? Marcus just happens to be a match for the transplant? Yeah, don't worry about tissue rejection or anything! Plus, are we to seriously believe that the Resistance doctor can do a transplant in an open tent in the desert? Where is Connor going to get the anti-rejection drugs if, as was mentioned earlier in the movie, regular anti-biotics are in short supply? Hollywood seriously needs to learn the difference between "suspension of disbelief" and "unbelievable."
This is the only Terminator movie rated "PG-13" instead of "R" which means they intentionally toned the violence down from previous installments to reach a larger (younger) audience. This is also the only Terminator story in which there is NO time travel. That's right, no electric spheres that leave round cut-outs in whatever the touch dropping naked Terminators into Los Angeles. It is unclear whether or not this movie takes place BEFORE SkyNet develops time travel or not. But somehow it just doesn't feel like a Terminator movie without that plot element. Actually that would be my overall complaint about this movie - it simply doesn't feel like a Terminator movie, and it isn't delivered as advertised. But I'm sure they'll probably make another one - they certainly left the door open to it at the end.