How was the Assyrian Empire unique?

The Assyrian Empire existed from the 14th to 11th century BC.  They first conquered Mesopotamia after the Akkadians fell and again after the fall of the Babylonian Empire.  Their empire stretched from Mesopotamia (today's Iraq and Iran) to Egypt.
One thing that makes the Assyrian Empire unique is that was the first empire in Mesopotamia to use iron weapons.  With their superior weaponry and large standing army, the Assyrians were able to conquer and maintain a large empire in the Middle East.
Another thing that makes the Assyrians unique is their infrastructure.  Several cities grew during the Assyrian Empire's reign in Mesopotamia including Ashur and Nineveh.  Roadways connected the main cities of the Empire which encouraged better transportation and communication.  Aqueducts and canals were built to make better use of water resources, allowing their cities to grow further away from the Tigris and Euphrates Rivers.  Later civilizations would make use of roadways for better communication and transportation, like the Persians under Cyrus and Darius, the Romans, and the Inca (among many others).