Put simply, I'm not sure what I feel about it. I haven't had much time to analyze the details. My initial reaction was "But the government didn't say it was a tax, they argued they have the right to mandate that the public purchase insurance under the commerce law." So, I was pretty surprised by the decision, as were most people notwithstanding whether they lean left or right.
As a primer to learn more about the decision and the law, here is a link to Tyler Cowen. He also links to several other comments.
More to come.