But two other groups are critical to the program's success: Healthy uninsured people, many of them in their 20s and 30s, and insured people who will switch over from existing individual policies.
Healthy individuals are needed to help pay for the sick.
And with instant feedback via social media, reviews by people switching from existing individual plans could define early consumer sentiment.
Some of those transitioning will be looking for better deals. Others will be there because their insurers canceled policies that didn't meet the law's minimum standards, and they may be upset.
Consumers don't have to decide on Oct. 1. You have until Dec. 15 to sign up if you want coverage by Jan. 1. And you have until next Mar. 31 if you want to avoid penalties for 2014. Fines start as low as $95 the first year but escalate thereafter.
Procrastinate beyond Mar. 31, and you'll have to wait until the next open enrollment period in Oct. 2014, unless you have a life-changing event like job loss, divorce or the birth of a child.
Former Medicare chief Mark McClellan, who oversaw the rollout of seniors' prescription drug benefits for Republican President George W. Bush, says his advice is not to sign up right away, but not to wait too long either. In other words, check things out. Buying health insurance is not as simple as shopping on Amazon.
"This is a milestone along the path but by no means the end of the road," said McClellan. "There's a lot more of a journey to see if it can really succeed."
Three key things to watch for are premiums, choice and the consumer shopping experience.
Premiums so far are averaging lower than what government experts estimated when Congress was debating the law. That's important for policy types, but it may not mean much to consumers. Current low-cost individual market policies are difficult to compare with the new plans, which offer better financial protection and broader benefits.
Plan choices seem adequate, but networks of hospitals and doctors may be tightly restricted to keep premiums low.
The biggest unknown is how consumers will feel about the whole experience. Many will be unfamiliar with health insurance basics, and applying for subsidies may feel like plodding through tax forms.
Still, after years of polemic debate and a Supreme Court decision -- and even as congressional Republicans keep trying to repeal it -- "Obamacare" will finally be in the hands of American consumers.