Here's a summary from JAMA:
The Affordable Care Act has made significant progress toward solving long-standing challenges facing the US health care system related to access, affordability, and quality of care. Since the Affordable Care Act became law, the uninsured rate has declined by 43%, from 16.0% in 2010 to 9.1% in 2015, primarily because of the law’s reforms. Research has documented accompanying improvements in access to care (for example, an estimated reduction in the share of nonelderly adults unable to afford care of 5.5 percentage points), financial security (for example, an estimated reduction in debts sent to collection of $600-$1000 per person gaining Medicaid coverage), and health (for example, an estimated reduction in the share of nonelderly adults reporting fair or poor health of 3.4 percentage points). The law has also begun the process of transforming health care payment systems, with an estimated 30% of traditional Medicare payments now flowing through alternative payment models like bundled payments or accountable care organizations. These and related reforms have contributed to a sustained period of slow growth in per-enrollee health care spending and improvements in health care quality. Despite this progress, major opportunities to improve the health care system remain.