Saw this film earlier. It was about as bad as I expected, but I was surprised to see a few things that worked.
Arnold as an aged Terminator worked much better than I thought it would. He's still tough, and is far more restrained than T3 when it comes to humour. His fatherly role was not exactly new ground, but the film managed to squeeze some new material out of it. He played Arnie's new role as gadget man and voice of exposition was a decent turn for the character, and his aging/breaking down between time travel jumps was kind of melancholy and sweet at the same time.
JK Simmons was great if under-used. I liked Jason Clarke as John Connor and the villain later, though what he became was so unclear it was hard to get a read on the character. The effects were great for the most part, really impressive compared to the trailers. There are some fun sequences and details. future stuff, Arnie vs. Arnie, so cool to see the time travel device for the first time etc.
Sadly, there is a laundry list of problems that squash any potential the film had.
The script is pretty dire. Time travel needs to make some kind of sense, at least in the context of the story, and the film doesn't even try. Nor does it try to establish any rules so the audience can understand the stakes. The hero plot is the same as always (note fate, lets blow up skynet!) with absolutely no attempt to be inventive; only it's picked up a lot of convoluted time travel baggage this time around. There are a ton of recycled ideas at play here, and not just in the direct homages.
Courtney is as terrible as everyone expected. Kyle is now a *****e, and has no chemistry with Sarah. This is a film derailing issue. Speaking of Sarah, Clarke was okay but never quite convinced as a tough as nails character. Seeing these new guys next to the mainstay Arnold just serves as a constant reminder of the original faces from superior work. By the same token, the film is slavish to some continuity details but tramples others. It all amounts to a sense of artefice throughout. It's like fan fiction.
All in all the film was bad, though not as bad as Salvation. With a tighter script and another actor playing Kyle Reese, this could have been a solid movie.