To be honest I was not to sure about part 1, it did not really grab my emotions, or involve me to much. It was an interesting scene and experience, but I never felt that connected with Julie.
This changed in part 2, where we see so much more of her as a person, see her being driven to pursue and explore these strange and shocking new desires and experiences. Seeing the work, dedication and time she has put into this, her feelings and need for this, it helps me to connect with her and to her.
Beyond that, once things start, I enjoy the sense of mystery, we don't know what is coming even though she does. Also the story does a very good job of describing the mechanical helplessness and heartlessness that is at work here
I am not quite sure how I feel about the emotional tone at the end, it was an amazing experience, but also it has left her rather broken and empty. Not quite as happy as I would have looked for personally, but her desire to push and take this further is interesting, and I must admit that I am curious to see what comes next.
A couple of thoughts, if you are interested. Firstly, it seems a shame to leave her breasts, and perhaps other parts, alone while she is being ravished by the machine. Also how about more randomness in the program? More than just random lengths of pauses, some random ordering and numbers of repeats, to make this more uncertain and thus interesting.