Many are still unhappy with Obamacare.
The main intent of the Affordable Care Act was to expand the safety net (Medicaid), regulate the non- employer-based private insurance market (the insurance exchanges) and help people buy that insurance (subsidies) in order to reduce the number of Americans who are uninsured.
On those metrics, it appears to be succeeding.
First and foremost, Obamacare was about improving access to healthcare. While it did improve access to insurance, in many, many other ways the United States is falling short. Things are likely to get worse before they get better.
Even with Obamacare, the Unites States still ranks poorly among comparable countries in insurance coverage. Even in 2016, when the rate of insured is the best it has ever been in the United States, Americans still have a greater percent of the population uninsured than pretty much any other industrialized nation in the world.