From the monumental failure of the initial government website for the federal health insurance marketplace (healthcare.gov) to the looming employer mandate, the Affordable Care Act has garnered its fair share of criticism. Yet, the ACA has withstood numerous legal challenges and changed the face of health care in the United States.

The most important change is perhaps the number of Americans who have enrolled to receive health insurance in the federal and state marketplaces, currently estimated at more than 8 million, along with millions more who are eligible for the expanded Medicaid program enacted by 27 states. These individuals now have the ability to seek medical care at negotiated rates, reducing the likelihood that they will seek health care through a hospital’s emergency department or require charity care.

Further, the rules for health insurers have changed dramatically. Individuals cannot be denied coverage because of a preexisting condition. Policies cannot impose annual or lifetime limits and are more comprehensive, with most offering minimum essential health benefits.

Health care delivery and payment models are also changing. The advent of Accountable Care Organizations and the proliferation of "narrow" insurance networks are results of the ACA. Fee for service is making way for bundled payments, requiring providers to adapt to new payment methodologies.

All of this comes at a cost. High wage earners now pay more in Medicare employment taxes. Certain individuals who elect not to buy health insurance will pay penalties next year. Soon, employers of 50 or more will be mandated to offer employees health coverage.

We have witnessed monumental changes since the ACA was enacted four years ago. The next few years promise further evolution for the entire health care industry, from patients to providers, and from private payers to government programs. Hold on, we are only halfway through the ride.