Terminator Salvation

Time-travel and its implications in films usually result in severe brain strain. This is particularly true of the first Terminator film, and the subsequent sequels and spin-off TV series have only made matters worse, as cyborgs and humans are continually sent back to the past in order to alter the future. Terminator Salvation takes place post-Judgement Day (i.e. T3) but before the advent of the T-800 (Arnie in T1) Not that Skynet's creations are primitive. The Terminators themselves are on the clunky side but are nevertheless alarmingly persistent and difficult to destroy. Furthermore, in this apocalyptic landscape we see that machines menace land, sea and air, killing and "harvesting" humans. The T-800 *does* put in an appearance late on, which isn't as jarring as I feared (a bit unnerving yes, but not film-destroying)
The onset of a headache begins early. John Connor listens to tapes made by his mother, telling him what he must do in the future (now) in order to ensure the survival of his father and therefore his own birth. He must save the young Kyle Reese, the father who is almost young enough to be his son. This is the point at which thinking about the plot becomes a seriously BAD idea, though the meeting between the two does have an emotional impact. Kyle is awed at meeting his hero, yet John is looking at a blood relative, who he knows will die saving his mother Sarah. One would imagine all this presdetination would make for a tension-free plot, but because each instance of time travel somehow effects future events, there's a genuine sense of danger for both John and Kyle - especially as it becomes clear that Skynet is actively hunting the pair. One of the best things about the film is watching Kyle grow up, from a scruffy boy scavenger to a young man showing leadership qualities.
Then we have Marcus, first glimpsed on Death Row receiving a visit from Cyberdyne, and clearly not surviving to 2018 by any normal means. His indestructability is gradually revealed, although he suffers cuts and bruises like anyone else, so the final reveal isn't exactly a surprise. It does, however, raise the question of what it is to be human. Marcus thinks he's human and his anguish as realizing the truth is palpable. Pointedly referred to as "it" by the resistance, Marcus as half-machine is actually more human than when he was 100% flesh and blood. John has a vested interest in wanting to rescue Kyle (his life depends on it) whereas Marcus wants to save the boy who helped him. Things get horribly muddied when the talk turns to Cyberdyne/Skynet programming - far too many unanswerable questions occur to the audience - and the first resurrection smacks suspiciously of cheating. Ultimately though Marcus' redemption is surprisingly poignant and brings with it a real sense of loss.