Destroying the statue of Sauron is this for the Outcasts. They may be driven out of their land and many of them enslaved, but their escape is accompanied by a symbolic strike which shows they are not helpless in the face of evil.
Then, directly after The Hammer kills Ratbag-
Hammer of Sauron: Now, bring me the head of this Gravewalker!
The Tower of Sauron:Bow to me, and I will deliver you to the Dark Lord unspoilt.
Celebrimbor: We bow to no one.
Talion:(deadly serious) Stand up, and fight!
Talion's victory over the Black Hand is this. Doubly so if it's actually Sauron in disguise. Talion may not be able to defeat Sauron himself but he's ground the Dark Lord's progress through Mordor to a halt. He's destroyed three of his high-level lieutenants and sewn massive chaos through the orcish ranks. While it may/may not stop Sauron's overall plans for the foreseeable future, it is enough for the ethnic inhabitants of Mordor to flee to safety. Note that he did this with only the Wraith and his mind control powers at his side.
Discovering that the Wraith stole the newly-created One Ring from Sauron's tongs, right in front of him. The sheer mithril balls on that elf.
The Bright Lord DLC, set before the main game, has several given that it involves the Wraith - armed with The One Ring itself - challenging the Big Bad:
The fight himself. First, Sauron doesn't seem particularly difficult, seeing as he doesn't do a lot of damage and you've got five warchiefs fighting with you. Then he cancels your brainwashing and you're left with five pissed off Warchiefs to fight at the same time. Then he comes back, THEN he resurrects the warchiefs you just killed and he might do it a few more times. He's not called The Necromancer for nothing.
The final cutscene definitely serves as one of these.
The Nemesis System itself can be considered one for Monolith Productions. The sheer amount of artistic design alone to make each Captain look somewhat unique and have a logical title was probably enormous. And yet not only did they pull that off...
The nemesis system allows for plenty of moments of unbridled awesomeness, not just for yourself when finally taking down captains who've been giving you trouble (or even when it's too easy), but also those for the orcs themselves. note An example of ease? Say three captains are stationed in the same stronghold, and while one is vulnerable to archery, another one is vulnerable to mounted beasts, and the third is afraid of fire. Solution? Ride into the stronghold on the back of what is essentially the saber-toothed tiger's bigger, angrier brother, using archery to open the pens of similar beasties. Then, after riding down the orc who is vulnerable to beasts (and is likely also terrified of them), you can then pick off the one vulnerable to archery immediately afterwards, with no need to dismount, and then hit an exploding barrel to rattle the pyrophobe, and then ride him down, peppering him with arrows as you approach. With the proper setup and planning, and perhaps a little random luck, you can kill three captains in as many minutes, then go and claim your runes when you're done. This game gives you the power to create your own awesomeness at will, if you know to use it.
Related to the above: any moment you succeed in clearing the entire orcish chain of command in any given area, from warchiefs to the lowest captains. Sure, they can repopulate the hierarchy over time, but you've essentially proven that, no matter what happens, you can easily wipe them out again... and again... and again...
Even better if you start with every spot on the board being occupied and empty it without time advancing. This essentially means that you can start at sunrise and hunt down every captain and warchief in an area before sunset, or doing the same in the span of a single night without being killed once. Once you pull this off, you prove that nothing the Orks can do will be able to stopTalion.
Any time you go hunting for a particular leader, in fact. Once you get properly leveled and get the hang of the combat system, it's entirely possible to waltz into a fort, kill so many orcs that you'd be standing atop a pile of corpses (if they didn't fade away), kill or brainwash every captain in the area, and leave without getting taken down once, proving just why the orcs fear you. It gets even funnier if you're hunting for a captain with a weakness to archery and pull an Indiana Jones while he's charging at you.
Freeing captured slaves from a band of orcs, especially if the orcs number into double-digits, without dying.
The final slave rescuing side-mission is one big trap, but Talion goes in to rescue the hostages anyway. This inspires the slaves to rebel, break their bonds, and fight back; it's part of the mission quest and you end up defeating an entire army with the help of the slaves.
When you finally obtain the ability to ride a graug. Nothin' like rampaging through dozens of Uruks on the back of the Rancor's big brother!
Brutalize kills. The fact that it sends even the bloodthirsty Uruks to flee in fear is enough to speak of Talion's badassery.
Forging the complete weapon legends of Urfael, Azkar, and Acharn is nothing short of absolutely satisfying. These are the legendary weapons of the Gravewalker that accomplished incredible unnatural feats and struck fear into the hearts of Orcs/Uruks all over Mordor. Considering the ending, they might as well be on the level of Narsil itself.
Liam O'Brien's performance as Gollum as a whole is this. His impression of Andy Serkis is so spot-on that many fans of the movies/game never realized that this wasn't Andy, but someone completely different, until they were told otherwise.