Transfer rates: USB 2.0 offers transfer rates of 480 Mbps, and USB 3.0 offers transfer rates of 4.8 Gbps — 10 times faster.
Addition of another physical bus: The amount of wires was doubled, from 4 to 8. Additional wires required more space in both the cables and connectors, so new types of connectors were designed.
Power consumption: USB 2.0 provides up to 500 mA whereas USB 3.0 provides up to 900 mA. The USB 3 devices provide more power when needed and conserve power when the device is connected but idling.
More bandwidth: Instead of one-way communication, USB 3.0 uses two unidirectional data paths, one to receive data and the other to transmit while USB 2.0 can only handle only one direction of data at any time.
Improved bus utilization: A new feature was added (using packets NRDY and ERDY) to let a device asynchronously notify the host of its readiness.