Shadow of Mordor has created an emergent gameplay system that allows the game to explore a single theme in depth, the nature of revenge.
I just got the Brand ability, which allows me to take over the mind of an orc and have it fight for me. I can do this easily mid-combat, so I can very quickly turn a horde of enemies against itself, then stand back and watch the battle. I also got the Shadow Kill ability, which allows me to teleport to any orc and instantly kill it. Or I can use my flaming arrows or my "infinite executions." These are all late-game abilities in Shadow of Mordor that make it easy to slaughter countless orcs. The horde that once frightened me, that I once ran from on a regular basis because it was too much to handle, is now my playground of death and decapitations, made even more fun by the fact that reinforcements just keep showing up, so my genocide never has to end.
When a Captain shows up (a named orc with special strengths and weaknesses that make him more challenging), I'm not intimidated by his taunts as I was in the first hour of the game. Instead, I charge at him. Setting him on fire, teleporting in for the kill, hacking at him on the ground, then picking him up and shanking him in the back until I finally slit his throat. So much for all that big talk. When another Captain shows up, I relish the chance to destroy so much of the orc command hierarchy in one fight. So I charge at him, setting him on... and I died. Turns out he was invulnerable to ranged attacks. He also shot poison arrows faster than a normal archer, and I was hit by both shots in less than a second, killing me instantly. Me. The man who just killed a hundred orcs and turned another hundred to my side! Literally dead before I even knew what hit me! But that's Shadow of Mordor: a power-fantasy rooted in failure.
The overarching narrative is a pretty typical revenge story. You are Talion, and your family is killed by Mordor minions. However, you survive to hack and slash your way through the land until you... kill the guy that killed your family? I thought I did that at the halfway point. Kill every orc? That seems impossible. Destroy Mordor? That's even more impossible. The specifics of your revenge are nebulous at best, but that's okay because the game's highly touted Nemesis system gives you plenty more excuses for revenge by facilitating the creation of your own emergent revenge story.
The Nemesis system refers to the game's ability to keep track of who killed you and the fallout from their victory. The orcs have a surprisingly defined hierarchy of power, and they all want to be at the top. Those on the bottom rung of the ladder will be promoted to fill any void that you create, and the orcs will even challenge each other in order to move up the ranks. Those that kill you become stronger, and the next time that you meet, their taunts will be more specific. They remember their victory, and they lord it over you, confident that they can repeat it.
At its core, Shadow of Mordor is really a series of interlocking revenge stories: The player kills one orc only to be killed in turn by another. Thus, motivating the next kill and setting the player up for the next defeat. Sometimes you can kill a Captain without issue, as I described above. Though at the best of times, when you're killed multiple times by the same orc, fueling his promotion from mere Captain to full-on Warchief, and he becomes a genuine threat to even a late-game Talion, then the Nemesis system shines as a storytelling tool. It allows the game to explore the nature of revenge and the imbalance of power inherent in such a relationship.
At that point, you cease to simply play the game, and you start conversing with it. With every loss, the game argues for your lack of competence, of skills, your weakness and ineptitude. With every win, you argue for your strength, your competence, and your prowess over the game and its systems. It's an argument that can never end because both sides are right: You are weak because the revenge-fantasy is rooted in defeat. The revenge-fantasy is not simply a power-fantasy, but an underdog-fantasy. Naturally our underdog always wins, but our victory doesn't necessarily come from brute force, like it would in a typical power-fantasy. Sometimes victory comes from cleverness or even dumb luck. But does your vengeance count if your nemesis never sees you coming, never knows it was you who killed him, never begs for his life; or if he's killed by another Captain in a territorial dispute? Is a death all that is required for revenge, or does that death have to be dealt out in a certain way?
Shadow of Mordor has created an emergent gameplay system that allows it to explore a single theme in depth. Appropriately enough for gaming, a medium that has always given its heroes more than one life, it's a theme that requires us to die and lose and fail, again and again and again. I'll always remember that no matter how many orcs that I decapitate. I'm only ever just two poison arrows away from death.