Has Medicare remained unchanged?
It depends on which aspect you're asking about. The big thing is that you MUST get on it at 65 if you want insurance. No private company is allowed to write you health insurance (or continue any policies you may have) once you reach that age (they do write supplements, or Medigap policies). Talk about interference with contracts
Other than that... there's always changes, but they're less cosmic than Obamacare was compared to what went before. For example, Part C (the Medicare Advantage privately run alternative to government Medicare) has had about 7% pulled from its budget. And, if you've had a good year, the amounts you pay for basic Medicare have gone up quite a bit.