Apple deleted my previous posts but I'll write it again:
I had the same problem. Tech Support asked me to try "solutions" (clean the camera, try new user, check utilities, etc.) nothing worked. They told me that it may be a software problem that would be fixed in the next upgrade. BUT afterwards they admitted that it's a hardware issue and that this model was "designed" to only perform in good quality under very bright environments. Their suggestion was to use the camera in a room with lots of natural light. I live in Germany, we don't have lots of bright sunlight most of the year. Absurd!
Today I went to the apple store and the manager said that the camera is the same as previous models, but the image looks bad because the new screen is soo good that we can see more details /defects now. "What do you want us to do?" - he asked- I suggested that the least apple should do is to provide us with an external -better quality- webcam. He told me to go next door to an electronics' store and buy an external camera by myself, or buy one in amazon. Unbelievable!
I said then apple shouldn't put in their publicity the sharp FaceTime example image (see below), because that is fake publicity. And you won't believe what he said: "it's a publicity image! of course is not real [...] everyone does it: mac donalds, coca cola, everyone!".
I'm speechless and extremely disappointed of Apple. It's seems they are trying to hide the issue as long as possible instead of admitting that they made a big mistake this time. Please complain in the official feedback site because they don't take this forums as an official complaint: https://www.apple.com/feedback/