Traditional Medicare plans typically force seniors to pay monthly premiums and deductibles for other medical expenses like hospital stays and prescription drug benefits. By contrast, seniors might pay a single monthly premium for a Medicare Advantage plan and have everything covered.

The downside is that these plans restrict which physicians a senior citizen can see and what hospitals they can use. Unlike most health insurance plans, many Medicare Advantage plans do not provide any reimbursement for out-of-network doctors or hospitals.

Such restrictions can be particularly dangerous if a Medicare Advantage patient is required to see a subspecialist when one might not be included on the plan. . . . .

"The biggest problem is that seniors usually are not educated and think they can go to any Medicare doctor, but they can't," said (Dr.) Verret.

Still, the lure of a single premium and a seemingly simple plan has been drawing new enrollees to Medicare Advantage. Roughly 25% of seniors were covered by these private programs in 2011, nearly double the number in 2004.. . .

In an attempt to get costs for Medicare Advantage in line with traditional Medicare, the government plans to force insurers to hit certain benchmarks to push costs down.

But there will be loopholes and rebates for "higher quality plans." What constitutes quality is still being determined and will likely leave a lot of wiggle room for potential winners and losers."