It's a long story, and I'm tired. But this was the 1st case in which the court decided, not just a particular dispute, but declared to power to void laws (or actions of the executive branch) if the court deemed them unconstitutional, i.e., the power of "judicial review." This is taken for granted today, and some would argue that it's always implicit in the fuction of the judiciary, but this was the 1st time in America the court declared explicity that it had that power. ("[I]t is emphatically the province and duty of the judiciary to say what the law is...")
And what made Marshall the tricky bastard that he was is that he did it under the cover of judicial modesty, in the course of denying that the Supreme Court had jurisdiction in a particular matter.
So he ordered no extra-constitutional remedy. But he laid the foundation for the court making stuff up in the future, e.g., right to abortion, a commerce clause that gives Congress the power to do almost anything, etc.
The trouble comes with the "[I]t is emphatically the province and duty of the judiciary to say what the law is..." language. Most parse that incorrectly, as taking the right to make law. But in fact, the only rational conclusion one can reach in the context of the case is exactly the opposite, that teh court only has power to interpret law, not to make it. As usual, people pull a sentence out of context, and spin it as meaning what they want it to mean. Not pointing a finger at you, BTW, the misreading of MvM is old as the case itself.