After looking at the Kaiser comparison of McCain's plan, I wandered over to McCain's site to read it in full, and make sure I wasn't just looking at a bad summary. Luckily, it was short. "Straight Talk on Heath Care," it's called. "John McCain is willing to address the fundamental problem: the rapidly rising cost of U.S. health care," which is quite brave of him. Also, not true.
It's another of these plans to sprinkle magical tax credits all across the land that will incentivize folks to buy less health insurance, but do absolutely nothing for the cost of care. Families get a $5,000 tax credit to help them buy insurance, and they can keep what they don't use, and so the hope is, they'll buy plans with higher deductibles, be unable to afford the deductibles, and will thus buy less care. It's like if I tried to make food cheaper by encouraging you to diet.
There's a bit more pabulum about encouraging price transparency and sound medical research (all good things, none of which are expanded into actual policy ideas on the site), and it does hint at removing the employer deduction for health insurance (which would be good in many ways, but is politically impossible), but at base, this is a big heap of nothing. It doesn't make health care cheaper so families can better afford it. It makes cheap insurance cheaper so families will buy more of that, and thus use less health care.