At the end of the opening sequence (in the nebula), the angel who will become the demon Crowley raises his wing over the head of Aziraphale to shield him from the 'raining' new stars. This is a direct reversal of the opening sequence of the first series where angel Aziraphale holds HIS wing up over demon Crowley's head to shield HIM from the first rains in the Garden of Eden.
When Aziraphale and Crowley are in Give Me Coffee or Give Me Death, the background music is a classical, instrumental version of Queen's "Bohemian Rhapsody".
In the opening sequence one of the sights seen are the 'Pillars of Creation' in the Eagle Nebula, in the Serpens constellation.