Okay so here's some of my amateur ratings of all four movies.
T1 was an action/scifi/horror movie. Without T2 it would have stayed as just that an action/sci-fi/horror film with a small but almost missed warning of man's arrogance in giving techonology too much free reign.
T2 was an action/sci-fi/horror movie with grand philosophical questioning about humanity and machinery and their relationship, could they find peace when it's man who is the most volatile or will there always be war? Such unexpected big-scale meaning in an action movie seems almost unheard of right? And that's one of the reasons we love it to this day. It basically spoiled us for the entire franchise in good ways and bad ways.
T3 was an action/sci-fi movie that fell short in capturing anything meaningful like T2 did, the only important thing you could take from this movie was that the ending served as the mind-^^^^ of certain things like the war with machines was always inevitable because of human error and negligence, something that never changes. Something about it made it miss the mark of still be considered truly a scary movie to me it was too much action not enough...something. Bad acting, bad directing, too gimmicky it was just an intended cash cow movie to me.
T4 was an action/scifi/post-apocolyptic movie that captured some of that sense of it being horrific b/c of the ruined-emptied cities and damaged landscapes and us walking through the movie really with Marcus. As the audience we're pushed into a landscape that like Marcus we're unfamiliar with, we've only seen it in books and in movies like he probably did and we know what a nuclear weapon does to the earth and sky because of those references like him, but Marcus sees, feels and walks through it so really he's the mind, body and senses of the film in this installment. The movie basically gave us more of an average Joe's POV of it with a few twists as his existence 15 years into a barely salvageable world for humans alters the timeline yet AGAIN. And of course there's the big philo-psycho-mind-^^^^ that if a machine can be more human like in T2, then what happens to the man who becomes more machine?
So for me:
T1 is 8/10
T2 is 9/10
T3 is 5.5/10
T4 is 8/10