What is unique about the V22 Osprey Aircraft?

The 'Osprey' has a pair of tilt-rotor propellers. Configured with one propeller on each wing, the rotors can then 'tilt' from the vertical position to the horizontal position, allowing the craft to hover or land an take-off vertically, like a helicopter.

Answer:

The fact that it's the only (first) tilt-rotor aircraft to enter service. The concept itself was tried and tested on numerous previous aircraft dating back to at least 1942.