T4 had potential but it should of been only like john connner rescuing kyle reese from the prison camp, and showing the horrors of the machine, tease a T1000 project. The whole Sam Worthington part was not needed
T3 was interesting only for completing the major types of time-travel story. T1 was a fixed loop. T2 was "screw causality, I'm cancelling the apocalypse!" T3 demanded a self-consistent universe: time travel had already happened, so it must eventually occur. Paradoxes are impossible --> paradoxes don't matter --> paradoxes get solved.
And listen - if Terminator 2 had sucked, we'd be just as mad about it screwing up The Terminator. 'It was a perfect loop! She had the Polaroid! How did any of that happen now? Whose kid is that?!' Fortunately, Terminator 2 fucking rules, so we just roll with the implication of disconnected parallel universes or whatever. It is genuinely difficult to care about the details when everything onscreen is so goddamn cool all of the time.
If Terminator 3 had been anywhere near that good, we'd also be talking about Sarah Conner's expectations as excellent philosophy but dodgy science fiction. But it's nnnot. It's a fat wreck of a movie that turns squeaky preteen delinquent badass John Conner into a whiny loser who does not deserve to be a protagonist. The bad guy is not as cool, because what possibly could be. The plot neither embraces the twist ending as a reveal or nudges the audience with dramatic irony.
It's five pounds of mediocre ideas rolling around a ten-pound bag. Then they filled the rest with bad CGI. T2 famously had very little CGI, because James Cameron was an effects dork who ascended to writer-director status, and he knew exactly what he could get away with. By 2003 the empty suits pushing this product already thought computers meant they could get away with anything.
It could've been good. It just super wasn't.
The what-if I like to pitch is that the resistance does not send back a terminator. They send back John Conner. So half the movie is Old John and Young John setting up post-apocalyptic supply drops and outsmarting some roving murderbot. Young John is still a drugged-out loser, but more the wiry conman type, dealing with PTSD and paranoia through stimulant abuse and identity theft. Old John is loving life as a mildly precognizant veteran in a city with only one unstoppable killing machine hunting him down.
The philosophical core of this nonexistent movie is that he is being handed more responsibility than any human being ever was, but that he has been uniquely prepared for that trial. His father was the most badass soldier of a ruined wasteland. His mom had the resolve to become a psycho guerrilla ready to fight god. His childhood was an anime assassin's backstory. And now he's being given a cheat-sheet for future events. He knows he survives, and that then, he has to come back here and do it all again. That is how much is required to save humanity from the machines.