I was trying to think of which games created certain mechanics that became popular and copied by future games in the industry.
The most famous one that comes to my mind is Assassin’s Creed, with the tower climbing for map information.
Then you will need to extend that to the OP of this comment chain as they didn’t specify either what Gears of War is. I am going to edit my comment to clarify but I do feel you are too pendantic for asking this.