The opinion, by Justice Scalia, is here. Justices Thomas and Breyer dissented; Justice Alito, joined by Chief Justice Roberts, concurred in the judgment. I’m reading the opinion now, and hope to have more to say about it soon.
UPDATE: Here’s a brief summary of the Justices’ views on the matter:
Majority (Justice Scalia, joined by Justices Kennedy, Ginsburg, Sotomayor, and Kagan):
(1) Video games are within the protection of the First Amendment, just as are other forms of entertainment (and entertainment has long been seen as constitutionally protected, partly because it can embody ideas, including political ones).
(2) There is no longstanding First Amendment exception that applies in this case, whether for depictions of violence, depictions of violence distributed to minors, or speech to minors without their parents’ permission. (The longstanding exception for distribution of pornography to minors does exist, but it must be limited to its historical scope, because the majority’s approach to the First Amendment exceptions is based on their historical recognition.)
(3) Given this, the law must be evaluated under “strict scrutiny,” a standard that the majority sees as extremely demanding.
(4) The law can’t be justified under “strict scrutiny” as being narrowly tailored to a compelling government interest in preventing harm to minors (the harm here is presumably the creation of habits and attitudes that promote criminal violence by children), because
(a) the evidence that the state gives for its claims that watching violent video games leads to bad behavior is inconclusive,
(b) the law is “wildly underinclusive” with regard to the interest given that it doesn’t cover other media that yield similar supposed effects on minors (similar according to some of the very experts whose work supposedly supported the law), and
(c) the law is “seriously underinclusive” with regard to the interest because it allows parents, guardians, and uncles and aunts to get the same supposedly harmful games for their children. (For more on how this sort of strict scrutiny analysis has worked in the past, including some criticisms of this general method, see my Freedom of Speech, Permissible Tailoring and Transcending Strict Scrutiny, 144 U. Pa. L. Rev. 2417 (1997).)
(5) The law can’t be justified under “strict scrutiny” as being narrowly tailored to a compelling government interest in “aid[ing] parental authority” by “ensure[ing] that parents can decide what games are appropriate,” because
(a) the industry’s voluntary self-regulation already “does much to ensure that minors cannot purchase seriously violent games on their own, and that parents who care about the matter can readily evaluate the games their children bring home,” and “[f]illing the remaining modest gap in concerned-parents’ control can hardly be a compelling state interest,” plus
(b) the majority in any event “doubts that punishing third parties for conveying protected speech to children just in case their parents disapprove of that speech is a proper governmental means of aiding parental authority.”
Justice Alito, joined by Chief Justice Roberts, concurring in the judgment: (I try to largely track, for this and later opinions, the numbering in the discussion of the majority opinion.)
(0) The law is unconstitutionally vague. Even though the standards of the law are borrowed largely from similar laws related to the distribution of sexually themed materials to minors (see Ginsberg v. New York (1968)), those standards become insufficiently clear when taken outside of the context of sex, given the difference in how sex and violence have been treated by America culture. (For more on this argument, and why I think it’s right, see this law professors’ amicus brief that I coauthored.)
(2) But less vague laws might well be constitutional, apparently because Justice Alito and Chief Justice Roberts would recognize a First Amendment exception, presumably based on a combination of the facts that (a) the law deals with videogames, which have special properties because of their intense interactivity, (b) the law deals with violent videogames, and (c) the law is aimed solely at distribution to children, and can be avoided even as to children if the parents or guardians get the games for their children.
Justice Thomas, dissenting:
(0) There is no need in this case to decide whether the law is unconstitutionally vague, because the claim hadn’t been discussed below. (Presumably under his view the vagueness question could be considered by the lower courts on remand.)
(2) There is a historical exception for speech to minors without their parents’ permission, because of Framing-era views related to the propriety of parental control over such speech.
Justice Breyer, dissenting:
(0) The law is not unconstitutionally vague, because it is similar enough to the law upheld in Ginsberg, and because “even when a precise standard proves elusive, it is easy enough to identify instances that fall within a legitimate regulation.”
(1 & 2) Video games are indeed constitutionally protected expression, and violent video games distributed to children don’t fall within a longstanding First Amendment exception.
(3) The law should therefore be evaluated under strict scrutiny, though a less demanding standard than that used by the majority — more a sort of balancing test, which will not lead to the nearly-universal invalidation that strict scrutiny has generally led to as to content-based speech restrictions.
(4) And the law is indeed narrowly tailored to a compelling government interest in preventing harm to children, because
(a) the law imposes only a modest burden (since it doesn’t affect adults, and it only affects those children who can’t get their parents or guardians to buy them the games),
(b) the studies are sufficiently persuasive evidence of the risk of harm to children that a legislature could reasonably conclude that a law such as this one is constitutional,
(c) the Court should defer to legislative judgment in this kind of situation, and
(d) the non-coercive alternatives to the law won’t serve the government interest nearly as well as the law would.