Short version: Terminator Salvation is great for the don't-expect-much-except-action-out-of-a-summer-movie crowd, not so great if you're looking for a worthy successor to the first two films.
Screen Rant reviews Terminator Salvation
For the record, I am not a McG hater, nor am I holding Christian Bale's set meltdown against him. I realize that McG will be forever haunted by the fact he directed Charlies Angels - but I had really high hopes for Terminator Salvation... I wanted it to be great.
Unfortunately, it isn't.
Why did I think that this long awaited addition to the Terminator movie franchise had even a snowball's chance of being awesome? Because I had the sense that McG wanted to prove he could do it. While many people think that his film We Are Marshall isn't all that great, I really enjoyed it and it demonstrated to me that he could actually do a film with characters you could care about.
But sadly, that's exactly what's missing from Terminator Salvation.
The film opens in 2003 with Marcus Wright (Sam Worthington) in a prison cell on death row, hours before his execution. He's visited by a scientist who has cancer (Helena Bonham Carter) and wants him to donate his body to science. She seems desperate to get him to sign, and he's not very cordial to her despite her situation and his.
The first problems in the film surface right at the start - why is she so desperate for him in particular to donate his body? Don't scores of people have organ donation cards in their wallets? And then there's his mysterious background - he's responsible for the death of his brother and two police officers... neither of these is ever explained in the film (nor in the prequel novel for that matter, which I did read).
From there the film jumps to some serious actiony goodness in 2018. I won't give anything away other than to say we get to see Christian Bale as John Connor almost immediately and he's involved on a mission that does not end up going very well. At all. Very satisfying first look at the future including some fantastic action and cool visuals/camera angles.
The upshot is that the resistance (not led at this point by Connor) has found a way to defeat Skynet. Connor volunteers to test it on a small scale before the big move against Skynet central. However that plot line becomes secondary to the story of Marcus Wright and his involvement with a young Kyle Reese (Anton Yelchin). For the non-fans out there, Reese is the man who was sent back in time to save Sarah Connor and is the father of John Connor. At the point this film takes place that hasn't happened yet (does your head hurt yet?).
Marcus doesn't seem to have aged at all although 15 years have passed, and there is a mystery surrounding him. He runs into Kyle and the young girl he's taken under his protection and very grudgingly goes along with them since he doesn't really know what's going on - and Reese did keep him from being killed by a T-600 (that's the bigger and bulkier predecessor to the T-800, aka the Schwarzenegger Terminator).
The film eventually brings together Wright and Connor via resistance pilot Blair (Moon Bloodgood). There's an issue of trust and conflict between the two that becomes the major issue in the film.