Justice Scalia filed a dissenting opinion which, to the extent that I understand it, I agree with. It's kind of confusing since you have to know exactly what Hamdi was asking, and I think the plurality opinion is right, as far as it goes—I think they are saying that the decision to make someone an enemy combatant must be subject to review—so I would have thought Scalia could concur with that while dissenting on the bigger point that THE PRESIDENT OF THE UNITED STATES CAN'T DETAIN PEOPLE INDEFINITELY WITHOUT A CRIMINAL SENTENCE OR CONGRESSIONAL SUSPENSION OF THE WRIT OF HABEAS CORPUS. But I guess Scalia has to dissent with the one step in the right direction that could be part of many more steps back.

... It follows from what I have said that Hamdi is entitled to a habeas decree requiring his release unless (1) criminal proceedings are promptly brought, or (2) Congress has suspended the writ of habeas corpus.

...

Many think it not only inevitable but entirely proper that liberty give way to security in times of national crisis—that, at the extremes of military exigency, inter arma silent leges. Whatever the general merits of the view that war silences law or modulates its voice, that view has no place in the interpretation and application of a Constitution designed precisely to confront war and, in a manner that accords with democratic principles, to accommodate it. Because the Court has proceeded to meet the current emergency in a manner the Constitution does not envision, I respectfully dissent.

—Justice Scalia