Just as a very bemused foreigner looking in - can somebody explain to me the negatives of "Obamacare"???

Over here we have had a government health insurance scheme for decades and although it's not perfect I'd prefer to get sick here than most other places in the world. From the very little I know, 'Obamacare' seems to be a similar system and many on this side of the pond are totally amazed at the levels of opposition to it.