"I have sought for some middle ground, which may at once support a due supremacy of the national authority, and not exclude the local authorities wherever they can be subordinately useful."
Letter to G. Washington, New York, April 16 1787
What is the difference? Oh, the pressure of a novelty (head bowed, finger tips to temples).
* It sought to structure an association of sovereign states.
* It did not provide for the establishment of a religion, as did many of the states, and three years into its existence flatly prohibited a religious establishment.
* It provided for the cessation of the slave trade.
* It assumed the debts entered into by the old confederation which had been incurred by the states, but which many of them were unwilling to honor.
But the important novelty was the idea that a central government would concern itself primarily with foreign matters and with relations between the states, and that the states would be concerned with domestic affairs.
Or as Madison described his vision before the convention:
And, as we know, the debates of the convention altered Madisons vision to a significant extent. His vision is found in The Federalist Papers.