We are not really sure that this is even a Terminator movie. Certainly there is no time travel in this film at all.
Okay. let's begin by looking at the various "Wha?"s in this movie. I'd like to start with Sarah. Of course, she does not appear because she died back in 1997. However, we do get to hear her on the tapes she left for John. The first one we hear is the one she was recording in the jeep at the end of Terminator.
In Terminator she clearly says "Tape 7, November 10th.". Here Sarah says "This is tape number 28." so that's wrong, she then goes on to talk about whether she should tell John about Kyle, however the dialog is very different from the original version.
Next let's move on to John. Here he is "John Connor, prophesied leader of the Resistance". Prophesied by whom? Has John been going around telling people he is the leader of the resistance and savior of mankind? People would think he was nuts if that was the case. Our understanding is that John Connor became the leader of the resistance by, you know, leading the resistance and leading it to victory. In Terminator Kyle says
...but there was one man...who taught us to fight. To storm the wire of the camps. To smash those metal mother-fuckers into junk. He turned it around...he brought us back from the brink. His name is Connor. John Connor...
In Genisys Kyle says
The first moment I saw John, he shot a terminator right in front of me. I didn't even know they could be killed. That was the first moment in my life I felt hope.
These don't sound like some "prophesied" leader but an actual leader.
In conjunction with that is the character of General Ashdown. Who is this? Why is there some sort of conflict between Connor and this guy? It's all fake and manufactured. Which leads directly into the resistance. Look at the first movie, living on the edge, in tunnels, minimal hardware, yet the humans eventually win. Here, they have submarines and helicopters and planes and on and on and on.
Also, Kyle gets upset because Marcus drew the HK's to them by his confrontation with the terminator in LA. However, no one seems very concerned that Skynet might be listening in their radio communications or triangulating Connor's radio broadcasts. Hmmmm?
And Marcus. Is this the origin of the T-800's? That seems to be what the movie is saying, but Marcus is not a T-800, he is something else. It's all very confusing. Also, in his past, John has dealt with at least one reprogrammed T-800, in Judgment Day and so knows that just because its a terminator does not mean its the enemy. Here he seems to have forgotten this.
And the digitally recreated Arnold is a joke. It looks so fake we couldn't believe it.
We could continue – Kyle and Star the only resistance in LA? – but we will leave it there.
Replace the Terminators with regular bad guys and this is a mediocre war-film.