I'm happy about the result but the opinion is a bit of a muddle--Substantive Due Process, informed by Federalism and buttressed by a novel Equal Protection analysis. The majority hold that an intrusion upon something that very much resembles the substantive due process of the Fifth Amendment makes the statute unconstitutional, though they avoid the label "substantive due process." The ruling then goes into a discussion of equal protection in order to make the Fifth Amendment right "all the more specific and all the better understood and preserved."
They begin with an inconclusive federalism analysis. The Court recognizes defining marriage is traditionally a state prerogative, then notes that the federal government has been allowed to make laws contradicting state law for a specific purpose related to a valid federal concern (immigration, social security benefits) then notes DOMA is very broad. Ultimately it dismisses the entire inquiry by saying it is unnecessary to decide if DOMA is a federal intrusion into state power.
Why? Because we are going to a substantive due process analysis that does not refer to substantive due process. The Majority says that New York's decision to recognize same sex marriage enhanced the status, dignity and protection of gay people. DOMA acts to take this enhanced status away, and the resulting injury is a deprivation of the liberty protected by the 5th Amendment. (Note that issues of federalism come in through the back door in order to help define the violation of liberty.)
One can understand the Court's reluctance to expressly rely on substantive due process because that doctrine requires that the liberty in question be some type of "natural right" inherent in our history and culture,while what is being taken away here is a brand new and historically unprecedented right Rather than address this issue, the Court says that the right to equal protection is "contained within" the Fifth Amendment's concept of liberty. In effect, the Court uses an Equal Protection analysis to bootstrap a Substantive Due Process violation
The dissent and the media talk about a new level of equal protection scrutiny, but this new level is never specified or explained in the majority opinion. The opinion states that mere animus cannot be the reason for discrimination and then says there is strong evidence that such animus was at least part of the reason for enacting DOMA. The huge scope of DOMA is considered further evidence of an intent to make a state's same sex marriages into second class marriages. The Court concludes that the principle purpose of DOMA is to impose inequality.
So is this new standard that a certain taint of animus in the enactment of a statute means it violates the EPC? No statement of which level of scrutiny applies is made. Since no consideration of other possible purposes the statute may serve is entertained, it is anyone's guess whether the standard applied was "rational basis", "substantially related to important state interest", "necessary for a compelling state interest" or something else.
In any case, since the Court held that the deprivation of liberty protected by the Fifth Amendment (specifically, the diminishing of the equal dignity that New York, in its sovereign capacity to regulate family life, decided to grant same sex couples) is enough to find the statue invalid, the entire equal protection discussion is arguably dicta (i.e non-binding analysis as opposed to new law).
On the other hand, since the SDP argument is weak without the EPC buttress, perhaps the EPC analysis is an integral part of the holding. If so, what is the future significance of this "taint of animus" version of Equal Protection?