It's not only A very unhealthy way of eating, it is THE most unhealthy way of eating. Atkins combined the obvious ie don't eat food processed with sugar or dairy/shortening (ie pasta, bread, cake, candy, etc) with the easy: meat.
What's really crazy is that he has cast the world's staples in a negative light: oats, rice, wheat and potatoes. These should be over 50% of most people's daily diets (without butter/sour cream). The rest should be fruits/vegetables.
Most dieticians would probably think meat at 10% is too high; I make a concession and go crazy on week-ends BBQing fish, chicken, steak, pork, etc., but I know not to do this more than 2 times per week.