J.K. Simmons was a highlight of the film, as he usually is, but his role was too small. I would've rather spent more time with him than with the much blander and less talented leads.
That would be an interesting take on how to do a Terminator sequel – tell it almost entirely from the perspective of a peripheral character whose life is affected by all the time war BS but who isn't directly involved. The implications of Skynet and the Terminators are terrifying, but none of the sequels have really been able to show that because the central characters just have too much knowledge and influence for it to be really effective.