I know the NHS has it flaws, but given the choice, I'd choose our healthcare system over theirs anytime.
The comments I keep getting from some American friends are:
it will be outdated, subpar, slow, it will drive away the brightest people of going into med school, taxes will be unbearable and prices of all other goods will go up, it will take out the motivation to innovate, ... (that's just from one discussion I'm in at the moment).