The cards can be discarded to, 'invoked,' to flip squares on the board, swap squares on the board, or shift rows of the board around. Cards in play have powers that are either unit rules, or that allow you to either swap or multiply invocations, and they also award victory points with the end-game defined by a rather traditional "first-to-ten" rule." Some powers, such as those of the Ghouls card are specifically about hand management. Others allow players to swap cards with opponents, and so on.
The board is made up of square tiles with a star-sign on each side, and a small graphic noting which star-sign is on the reverse of whichever side is up. Once the board has the correct patterns on it, when the stars are right, the Great Old Ones and their Lesser/Greater Servitors can be summoned, or put into play from the player's hand.
So as the entry on Board Game Geek suggests, the game involves: hand management, a modular board, pattern building, pattern recognition, tile placement. The fascinating thing about this game is both how well the mechanics fit the 'skin' or Mythos material which makes for the game's hook, and how transparent the mechanics are through that skin. It could easily be done without the Mythos skin, using geometric shapes.
Given that I'm biting the bullet with Titanomachia, and returning to a more traditional board layout of squares, I feel like this game is both where I've wanted to go, and also full of ideas that could be extended, built upon, or even re-purposed to the end of making a giant-robot dueling game that people without a giant-robot-boner could enjoy.