I don't know how to salvage this series. You can keep going back and rewriting things to erase the timeline from sequels, but after a while all of that becomes messy bullshit. If I were writing Terminator 3 I would have written it about other machines sent back to kill the Conners (and key people in the resistance, which is the one good idea T3 had), and ensure the creation/survival of Skynet. Sending one Terminator back wasn't enough; it would have had backup plans as well.
Things I would do/avoid:
- The villain needs to be scary/threatening again. Arnold in the original was great. Robert Patrick in T2 went in a totally different direction but was still amazing. Kristanna Loken in T3 wasn't threatening at all, and I felt like her robot/liquid metal design was a regression from the T-1000. Salvation didn't really have a villain (I think?) and I kinda liked the idea of John Connor being turned into a nanomachine robot in Genysis, but they didn't do anything interesting with it and Jason Clarke was rubbish. A female Terminator could be a good idea from an infiltration perspective, but T3 just fucked the execution.
- No more lame references to the original two films.
- I hated that the central theme from the first two films was "The future is not set. There is no fate but that which we make for ourselves", and the sequels (T3 specifically) shit all over that by making Skynet inevitable. And then it was an OS in Genysis for some reason? This is why having Skynet having taken measures to ensure its own survival makes a lot more sense.
- I don't think Salvation is a good film, but I like that it tried to move the series forward by not just being a remake of Terminator 1 again. Maybe setting a sequel in the future war again would be a good idea?
- No more Arnold, please. How about another big muscular guy as the principal enemy, or do what T2 and T3 do by actually changing up the villain? I loved how Robert Patrick just looks like an ordinary guy (the original idea for the T-800 in the first film), and he is friendly and his infiltration techniques are very logical (i.e. everyone trusts a policeman). And again, I don't think Kristanna Loken was right for the role, but a female Terminator could be an interesting idea.
- Please make James Cameron have a hand in casting. I think every main character they've cast since he left the series has been awful.
- I don't know how you'd get there from the timeline, but exploring the future war might be interesting. They've never really done this, and most of the ideas in Salvation were shitty.
- Please no more convoluted time travel shit like in Genysis.
Scientist Man explains it best.
Probably some other stuff, but I've not really paid attention to the series post-T3. Hated that damn film so much.