I am not an avid Terminator fan - I just went with friends to see what looked like a good movie. I was absolutely drawn in and spent the entire movie wide-eyed. I've never been to a movie where you felt the sounds of helicopter blades in your chest!
Non-stop action. I think the producers did great things with sound as well as visual effects, and it enhanced the whole experience. I can still hear the sound of the machines in my head the next morning.
I did find myself making comparisons to other movies: Fantastic Four, a hint of The Matrix, and hints of "I've seen this before" but I can't put a name on it. However, there were some good plot twists so that the movie was not entirely predictable.