I really don't believe people who say they are doing this diet and not feeling good. It's a healthy diet. The danger zone is that there is room for people to make really bad choices and eat foods that will "not make them feel good". I eat lean meat or fish and vegetables everyday, I eat a salad for lunch everyday. Bacon and Cheese and Eggs or an Atkins shake for breakfast every day. What is there not to feel good about? They've gotta be making bad choices and then blaming the diet for their bad choices. If you stick primarily to whole foods and take a multi vitamin, there is no reason you should be feeling bad on this diet unless something else is wrong with you and you should see a doctor.
Regular bowel movements are also important. That could cause you to not feel good. If you are not using the bathroom at least (bare minimum) once a day, you need to work on that.
Also, the people who say they did the diet before and didn't like it, and now they are back, I don't get them either. If you didn't like the diet the first time, why are you doing it again? There is more than one way to lose weight. Maybe this isn't your path.
Personally, even though I had a shaky week last week, because I didn't feel like cooking, I am loving my Atkins experience and I feel very good about it health wise.