I think that a person's experience of the NHS is going to depend on what they will need to use it for. For example, I have had a very positive experience of the NHS, but then I have never had to stay in hospital overnight, I have never had surgery and the only thing I usually need to see the doctor for is a repeat prescription of the pill.
The only time I have been to the hospital as a patient was when I broke my leg at age 12. We went to the emergency room, it was X-rayed and put in a cast and I went home - it was all sorted within 2 hours.
However, my brother has had surgery several times and if he didn't have special insurance for athletes, the NHS wait would have been months at a time. He's a national gymnast (he was the non-travelling reserve for the Melbourne Commonwealth Games last year) and the BAGA provides private insurance so he gets priority for sports injuries. In the last year, he's had minor keyhole surgery on each shoulder and one major operation on his right shoulder - had he not been able to get it fixed so quickly, he may have suffered irrepairable damage to his shoulders for the rest of his life (he has a tendency to overdo his training, especially on the rings, which is why the shoulders got so bad).