i think the reason that the heller decision doesn't come across as the landmark decision that it is, is because we've already been living in a post-heller world for some time now. we've all grown up with the general understanding that the constitution protected an individual "right to bear arms." at least that's what i thought before i went to law school. there i discovered that that constitutional right had never been recognized to exist by the courts. in fact, that understanding had been implicitly rejected a few times, most recently in the 1930s by a unanimous court.
also when i was in law school, i remember seeing a flier hanging on the wall for an essay contest sponsored by the NRA. the gun association was looking for essays from law students arguing that the second amendment did, in fact, guarantee an individual right to own firearms. just the fact that the contest existed was a remarkable tacit admission by the NRA of their legal predicament. can you imagine the ACLU using an essay contest to find a plausible argument that the first amendment protects speech?
meanwhile, if you had asked people on the street whether the second amendment guaranteed an individual right to bear arms, it would be hard to find someone who said it wasn't. chief justice warren burger once called that widespread belief "one of the greatest pieces of fraud…on the American public by special interest groups that I have ever seen in my lifetime." the NRA has long sold the public on the idea, sold so completely they didn't realize there was a sale. the only problem was that the common belief about what the amendment meant was completely out of sync with where the law actually was.
i saw that essay contest flier fifteen years ago. heller is the culmination of that effort by pro-gun activists to make the law correspond with the common understanding. because the groundwork for the decision has long been laid, it doesn't seem like anything actually happened yesterday. and it also conceals just how activist the majority opinion in district of columbia v. heller really is.
UPDATE: yale law prof. jack balkin says essentially what i was trying to say here, except he says it better. (thanks to dsc via email)