It's thinner. It's lighter. It's powerful-er. What else is it? Here's what we know from Apple:

Fully laminated, 7.9-inch (diagonal), 2048x1536 LED-backlit Multi-Touch display with IPS technology

Apple A8 SoC with 2nd-generation 64‑bit architecture + M8 motion coprocessor

8 MP iSight camera + 1.2 MP FaceTime HD camera

Wi‑Fi (802.11a/​b/​g/​n/ac) with dual channel (2.4 GHz and 5 GHz) and MIMO support + Bluetooth 4.2

19.32 Wh rechargeable lithium-polymer battery

Three-axis gyro + accelerometer + ambient light sensor

And a brand new model number: A1538