Here are some initial impressions of the Heller opinion, which I think was both the right result and rightly minimalist:
1. We're all originalists now. One of the most extraordinary things about this case is that it presented, for the first time in modern memory, a chance for the Supreme Court to decide the meaning of a constitutional right without a heavy overlay of "constitutional law" -- a body of relevant decisions from the Supreme Court itself. For "faint-hearted" originalists, like Scalia and others, the existence of non-originalist precedents can be a barrier to reaching originalist results. But here the issue was one of truly first impression, presenting a "clean" controversy. It therefore allowed the Court to address the issues on first principles of constitutional interpretation.
So what principles did the justices reach for? It's not surprising that Justice Scalia turned to the text and to originalist sources to determine the meaning of the words of the Second Amendment. And while the Stevens dissent makes noises about United States v. Miller as if it controls the outcome in favor of the constitutionality of heavy regulation of firearms, most of his dissent grapples with originalist questions. Stevens might not be a very accomplished originalist, or you might think he was wrong in this instance, but the mere fact that he and the three who joined him paid such obeisance to originalism on a matter of constitutional first impression confirms again its ascendance as a methodolgy.
2. Judicial scrutiny of the right. The Court does not tell us what level of scrutiny it will apply to restrictions on the right, but it does rule out rational-basis scrutiny. Op. at n. 27. (It also rules out "balancing." More on that below.) This leaves us, according to the Court, with either intermediate scrutiny or strict scrutiny. There will be a lot of argument in the coming years about this, but as between the two, based on this opinion I think the more likely scrutiny is the strict kind. The Court's opinion is quite exhaustive about the importance of the Second Amendment in preserving what it calls at various points the "pre-existing" and "inherent" right to self-defense. At least as to restrictions that go to this core self-defense aspect of the Second Amendment right, as contrasted with the use of guns for sporting and hunting purposes, which the Court does not address, it's hard to see the Court accepting any but the most narrowly drawn laws serving compelling justifications. There is no analysis in the opinion, for example, to suggest why this core aspect of the enumerated Second Amendment right should be given less judicial protection than the core of First Amendment or other enumerated rights. In fact, the Court explicitly compares the Second Amendment right to free speech, which all regard as fundamental. Op. at 62. It may be, of course, that there will be a larger number of "compelling" reasons for regulation of gun ownership (e.g., public safety) than of, say, speech. And that may mean in practice that state regulation will have an easier time passing strict judicial scrutiny. But the tone of the opinion suggests that the courts will have to take Second Amendment rights very seriously.
3. Limitations that are presumptively constitutional. As I read the decision, and especially the parts of the decision Orin has noted, several kinds of firearms regulations appear to be constitutional, at least as a general matter, whatever the level of scrutiny the courts settle on: (1) prohibitions on gun ownership by felons and the mentally ill; (2) prohibitions on gun possession in "sensitive places" like schools and government buildings, presumably including courthouses; (3) laws regulating the commercial sale of guns; (4) laws prohibiting the possession of unusually dangerous weapons, like sawed-off shotguns and machine guns; (5) prohibitions on carrying concealed weapons, which the Court describes as having been common and constitutional under Nineteenth Century case law; and (6) laws providing for the safe storage of weapons to prevent accidents (Op. at 60). The Court does not, of course, decide whether these restrictions are constitutional, and certainly doesn't give a green light to unnecessarily onerous forms of these restrictions, but broadly speaking they're probably acceptable. Note also that the Court's list of presumptively acceptable limitations is not exhaustive.
4. Some brush-clearing. While the National Rifle Association is already planning challenges to other gun-control legislation around the country, there is a threshold issue their briefs and lower courts will have to address. The Court explicitly reserved the question whether the Second Amendment is incorporated into the Fourteenth Amendment's Due Process Clause such that it operates as a restriction on the states as well as the federal government. Op. at 48 n. 23. I doubt this will prove an obstacle to challenges to state or municipal regulations, and the Court suggests it won't be, but it will have to be addressed.
5. Down with "balancing". In addition to rejecting rational-basis review of gun regulations, the Court also rejected a "balancing" approach to judicial scrutiny that has become popular among legal academics in other constitutional contexts like Equal Protection and substantive due process. The balancing approach was urged today by Justice Breyer in dissent, and was firmly rejected by Scalia. The approach would involve courts "balancing" the government's interests in regulation against the particular individual interests at stake in the asserted right, and then deciding, somehow, which of the two has more weight. The Court rejected this approach as basically indeterminate and "judge-empowering," since it operates as practically no constraint on judicial decisionmaking. Additionally, the Court notes: "We know of no other enumerated constitutional right whose core protection has been subjected to a free-standing 'interest-balancing' approach." Op. at 62. The Court then compares the right to the enumerated right to free speech, under which the Court would not engage in interest-balancing before deciding whether to protect the expression of unpopular views. I would add that balancing approaches are also unusually likely to favor government intrusion on individual rights, since the government often claims grand society-wide harms from the exercise of individual rights and timid courts often defer to legislative judgments about the seriousness and likelihood of those harms.
6. Unanimity at last. Chief Justice Roberts came in with the hope of producing more unanimous decisions from the Court. While today's decision was 5-4, it was actually unanimous on one point: there is an individual right protected by the Second Amendment. The split came over the important question of the scope of the right and whether the D.C. law itself was constitutional, but the underlying individual-right theory prevailed over a collective- or states-right interpretation that would give no single person the ability to challenge any type of arms regulation. Thus, an idea that not so long ago seemed radical and even frivolous to many academics and judges now has the assent of all of the Justices, representing a wide range of views about constitutional law and theory. And that leads to the final point...
7. Scholarship matters! I join others in congratulating Eugene, Randy, and many others for the influence that their own careful scholarship had on this decision, as evidenced by the Court's extensive and significant citations to their work.