The premise for T4 was OK; it was the execution that was bloody awful. A half-decent director rather than 'McG' was needed, as well as some actors with some decent acting chops, and a better script, if they wanted to successfully pull off the similar sort of tone that T2 had where Sarah was questioning whether a Terminator could actually do something good.
When watching T4 for the first time, it piqued my interest for a while. My interest dropped sharply with that scene were the truth is revealed to the character whose name I can't remember, the hybrid/cyborg, by Skynet. The actor's facial expressions mirrored my own, why is Skynet doing this stupid face-morphing thing exactly? Did they have a bit of CGI budget to burn?