Not as bad as people say it is. *Spoilers Ahead*
There we go, I said it. an ample sequel to Terminator 2 (following a slightly different timeline, hence how Sarah Connor is still alive whereas in T3 she wasn't) The film kicks off very quickly but gets carried away with the pace. very suddenly. It loses the character development that we needed to the point we care very little about Dani. Her father and brother die and we don't see a great deal of depth to the emotion and she quickly forgets that her family had just died hours previous.
The character, Grace, and the new terminator, Rev-9, were done well in my opinion. I felt their characters were interesting and they were acted out well.
The CGI, aside from about 5% of it, was immaculate, particuarly the beginning sequence where Sarah Connor is explaining what happened to John after Judgement Day. The Rev-9 morphing was amazing too which is something the film doesn't get credit for.
Whereas the script is great at times, it lacks big time in most of the film. which lets it down quite a bit, especially seeing as the film itself was quite long.
The music and tone was also off at times. Aside from the beginning, and the reveal of Arnies character, they missed the tone that makes the Terminator 1 and 2 so great.
all in all, it was a decent film. It was nice to see some of the original cast back together. The film fell short in Music, Script, Main character, character developement of the new characters and pace. The film exceed in its visual effects, action and what I thought was an interesting timeline