According to GameStop UK’s store page Middle Earth: Shadow of Mordor is due to be released on the 29th of August. The page lists all versions of the game with this release date except for the PS4 version.
It was known that the game was coming out this year but an official release date was not yet set. It seems appropriate for it to be released in August to avoid the big AAA games that are being released in the later months of the year.
