The reason for such unique electronic properties is that electrons in this material are very different from those in any other metals. They mimic massless relativistic particles – such as photons.
Due to such properties graphene is sometimes called 'CERN on a desk' – referencing the Large Hadron Collider in Switzerland. This is just one of the reasons why the electronic properties are particularly exciting and often bring surprises.
In contrast to the single-particle picture, the real spectrum of graphene is profoundly nonlinear so that the Fermi velocity describing the spectral slope reaches ~3x10^6 m/s at n <10^10 cm^-2, three times the value commonly used for graphene.