I've done the ketogenic diet several times and had really good luck with it for losing the stubborn belly fat around my torso and hips. I do find that on about day 4/5 I feel pretty lethargic and my performance in workouts decline, but once I'm fully in ketosis I don't see any decline in my performance.
Detractors of the diet worry about heart disease with the high cholesterol/saturated fat consumption required in the diet. There is now research suggesting that saturated fat/cholesterol is not to blame for this. Cholesterol levels in your blood can be altered by your diet, but by far the biggest factor is genetics. The problem is inflammation- Cholesterol binding to the walls of arteries to help repair them when they are damaged. No matter whether you have high cholesterol or low cholesterol, everyone has high enough cholesterol levels in blood to cause artherosclerosis if the arteries are damaged
It is certainly still up for debate. It is my personal opinion that added/processed sugar in our diet is a major cause. While I was doing my graduate work at Colorado State in Anatomy/Physiology, we covered this topic extensively and I found the divide between some of my professors on this issue fascinating.
Related reading:
http://circ.ahajournals.org/content/103/25/e132