A recent study of British expats found that approximately 20 percent of them believed that their health had declined since they moved abroad and they have linked that decline to the standard of healthcare in their adopted country, most saying not only was it very different, but very inferior to that provided in the UK.
Of course this survey is ultimately inconclusive, it is from a small number of the total of Brits abroad, and it is mainly taking a British perspective of foreign healthcare, and to be truthful the British perspective of the rest of the world has never been that great, nor that trusworthy. It also doesn't ask what anyone from abroad thinks of the British system.
But all this is immaterial as the simple fact is that if the Brits abroad don't like what is offered, then they will not be happy, and move somewhere else. The simple fact is that if people want to have medical treatment at a level which is comparable to that of the UK, it is there, you simply have to look for it, or get somebody else to do the looking for you.
Most International Health Insurance Companies based in Britain have global partners affiliations and they will know which of the country's available health services, is most to the satisfaction of their British people through a long process, simply in order to deliver the best service.
The one thing to stress here is planning, get all the important things done before you go, and yu won't find things quite so strange when you evenyually get to where you are going.