“It’s almost like trying to predict the local weather from national averages,” Mr. Altman said. “This is really now a state and local game, not a national one.”

Indeed, a review of state-by-state enrollment data and other research, as well as interviews with patients, advocates, health policy analysts, elected officials, supporters and critics of the Affordable Care Act, suggest that, for consumers at least, the state of health care under the national law depends almost entirely on where a person lives.

Some states have had a flowering of competition among insurers, including nonprofit co-ops — entirely new entities that are capturing the largest market share with low prices and remaking the coverage landscape in places like Maine. But in other places, including parts of states like New Hampshire and West Virginia, consumers have hardly any insurance choices at all.

The deep political divisions the law has engendered — just 38 percent of Americans view it favorably, according to survey findings released this week by the Kaiser Family Foundation — make assessing it a complex task. The evidence remains largely anecdotal; for every satisfied supporter, it seems, there is a disgruntled opponent.