Even more importantly for present purposes, the Court held that Common Article 3 of Geneva aplies as a matter of treaty obligation to the conflict against Al Qaeda. That is the HUGE part of today's ruling. The commissions are the least of it. This basically resolves the debate about interrogation techniques, because Common Article 3 provides that detained persons "shall in all circumstances be treated humanely," and that "[t]o this end," certain specified acts "are and shall remain prohibited at any time and in any place whatsoever"—including "cruel treatment and torture," and "outrages upon personal dignity, in particular humiliating and degrading treatment." This standard, not limited to the restrictions of the due process clause, is much more restrictive than even the McCain Amendment. See my further discussion here.
This almost certainly means that the CIA's interrogation regime is unlawful, and indeed, that many techniques the Administation has been using, such as waterboarding and hypothermia (and others) violate the War Crimes Act (because violations of Common Article 3 are deemed war crimes).