It is interesting to recall that when Charles was a similar age to his son he was held in very high public regard. It was - possibly - reduced by his somewhat enforced unsatisfactory marriage to a woman whose expertise in public relations massively outshone that of the family into which she had married.
I am not a monarchist - I would prefer a non-executive elected head of state - but do have some sympathy for the condition in which Charles finds himself. He is a man of some intelligence but has never been permitted to put his intelligence to any real use. He has - in effect - been held under some condition similar to house arrest for pretty much his entire life just waiting for a single event. His constitutional responsibility has been to amuse himself doing nothing controversial until his mother dies.
I agree - and we should remember that Charles and Di were the media darlings at a similar stage in their lives in terms of marriage and kids as William and Kate are now. I think it is very difficult to retain that public affection year after year, decade after decade while waiting for the job you've been born to.
And there lies a warning to William - assuming Charles lives as long as his father (and why shouldn't he), William has another 28 years to wait before becoming King. Will he still be popular by then, will the intervening years of a non-job corrode public respect and affection? In 2050 will the public want the 35 year old George as King rather than the 66 year-old William.
Longevity and good health are a real problem for the royals now as it likely means we will have a series of short-is monarchies with the monarch already fairly elderly before attaining the throne and having really not had a job for decades.
