The graves are certainly royal. The faces of the men are not all covered with masks. That they are men, and warriors, is indicated by the weapons in their graves. The quantities of gold and carefully worked artifacts surely denote honor, wealth and status. The custom of clothing leaders in gold leaf is known elsewhere; for example.
In the latter 20th century and the beginning of the 21st century, the authenticity of the mask has been formally questioned. The magazine, Archaeology, has run a series of articles presenting both sides (see under External Links).
By the time of the excavation of the Shaft Graves, the Greek Archaeological Society had taken a hand in supervising Schliemann's work (after the issues at Troy), sending Panagiotis Stamatakis as ephor, or director, of the excavation, who kept a close eye on Schliemann.
The advocates of fraud center their argument on Schliemann's known reputation for salting digs with artifacts from elsewhere. There were many people on the site. The resourceful Schliemann, they assert, could have had the mask manufactured on the general model of the other masks and found an opportunity to place it in the excavation.
The defending advocate(s) point out that the excavation was closed on November 26-27 for Sunday holiday and rain. It was not allowed to reopen until Stamatakis had provided the work with credible witnesses. The three other masks were not even discovered until the 28th. The Mask of Agamemnon was found on the 30th.
A second attack is based on style. The Mask of Agamemnon differs from three of the other masks in a number of points: it is three-dimensional rather than flat, the facial hairs are cut out, rather than engraved, the ears are cut out, the eyes are depicted as both open and shut, with open eyelids, but a line of closed eyelids across the center, the face alone of all the depictions of faces in Mycenaean art has a full pointed beard with handlebar mustache, the mouth is well-defined (compared to the flat masks), the brows are formed to two arches rather than one.
The defense presented prior arguments that the shape of the lip, the triangular beard and the detail of the beard are nearly the same as the mane and locks of the gold lion-head rhyton from Shaft Grave IV. Schliemann's duplicity, they claim, has been greatly exaggerated, and they also claim that the attackers are conducting a vendetta.