What are the main issues with this PC port? I've read nothing but negative reviews and issues with refresh rate.

I had GPU encoding or whatever enabled at first because my CPU is my weak point, however I would get lag and slight stutter issues when turning the camera, especially outdoors. With GPU encoding OFF I'm having no issues, no frame drops.
What else can I expect? Does the game become harder to run as the story goes on?

460 GTX, E8400 3.0GHz here so I'm very, very surprised with my results.