The best Assassin's Creed game that's not an Assassin's Creed game, Monolith took influence from Ubisoft's open-world behemoth and bolstered it tenfold with Batman's Arkham combat, a cherry on top being the phenomenally original 'Nemesis system'. Built upon the guarantee that in any action game you're always going to die at least a handful of times, Shadow of Mordor makes that an in-game mechanic.
Where other developers reconcile making you start over, fail-states give you newly-empowered enemies who'll taunt you for getting the upper hand. By creating personal foes for every player, it means you'll get consumed in carving your own way through the enemy ranks for hours, interrogating lower-ranked goons to exploit weaknesses and fears in whoever brought you down in the first place. It's a superb system, factors directly into the story, and acts as something that gives Shadow more replayability than a vast number of releases this generation combined.
To this day, although Middle-earth's main influences are plain and obvious for all to see, the simple fact is hardly any games manage to deliver such a set of satisfying mechanics in such a downright fun package.