Middle Earth Shadow of Mordor
This game takes pretty standard open world mechanics and executes them well and then adds the unique nemesis system on top. This system has orcs who defeat you in battle remember encounters, get stronger and talk about the different things that have happened. In addition to this, you can dominate orcs later in the game to mind control them. This allows you to bring the orcs to fight for you and pit orcs against each other in various events. All in all, a fun game with some great ideas, it is unfortunate that the nemesis system was patented though so isn't used by other games.