These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: The Final Boss. While fighting through the Pelennor Fields, you suddenly get warped to the top of Barad-dûr, fighting the Eye of Sauron itself, and the ending monologue afterwards just rambles about how the Fourth Age has begun.
Crowning Moment Of Awesome: And Heartwarming- a random soldier in Helm's Deep mentions that the only thing he has to lose is his life, which he received freely and is more than willing to give in order to save others. the matter-of-factness with which this line is delivered is surprisingly poignant.
In Osgiliath, when Berethor learns that he's been brainwashed by a Morgul blade shard embedded in his body, he immediately goes about fixing it by grabbing a dagger and literally digging the blade out of his flesh.
Fan-Preferred Couple: A number of fans were pretty annoyed when Berethor/Idrial was sunk about half way through the game because apparently he was already married to Morwen.
There is absolutely no setup for this whatsoever besides a cutscene at the end of Osgiliath, and even that comes out of nowhere, given the last scene concerning this matter was in Rohan, where Idrial bitches at Berethor for helping Morwen and Rohan over the Elves-she's basically accusing him of being easily swayed by a pretty face.
Game Breaker: A lot. See below. Basically, everyone has at least one that can be abused for massive advantage.
Just pump stat points into Idrial's spirit stat, and she can average 20,000 damage a turn mid-game.
Heck, she has this move similar to Auto-life from the Final Fantasy series, except way more broken- when the party member it is cast on gets defeated, they are brought back to FULL HP AND MP, and that member gets to attack immediately.
And she can cast on herself. So if anything kills her she will instantly be brought back to life with full health and MP AND be able to cast it on herself again before anyone can attack her. You will only lose a battle in this game if you choose to. She can even use another move (with her restored MP) so she can attack and cast autolife on the same turn.
Berethor inflicts the most damage out of all the characters with his 5-hit melee combo. This only combines with his ability to tank hits with Taunt and buff allies with Leadership skills.
Company Might (Improves offence power) + Fellowship Grace (Restores AP). For unknown reasons, the former interacts with the latter to produce massive amounts of AP whilst both are active, giving you infinite AP. Good thing, too, as restoration items are a limited resource for some time, and even when they're not(which takes some grinding), require AP to make.
Add Royal Grace onto that for healing, and Idrial is hardly even needed.
War Cry makes 3 of your allies use their strongest attack on a single target. It only costs 200 AP, and the attacks are free (You don't get skill points for them though). With the right set of team mats and unlocked skills (Eaoden's Rampage of the Helm, Elegost's True Shot, Berethor's Gondor Rampage), this is the most damaging single "attack" in the game.
Hadhod can actually inflict more damage with his Spirit skills than Idrial can. Yes, this is a Dwarf who's a Magic Knight capable of wiping out entire groups of enemies, shield allies with his Mountain Shield, and still pack a mean punch with his melee skills.
Elegost has 2 big ones. True Shot, the final Bow Craft, is a Spirit attack that is capable of truly massive amounts of damage, at least 24,000 each shot. Boosted by Elfstones, and it begins to get insane. Arrows of Sleep is a Ranger Craft that you can actually get pretty early, and it starts a pretty mediocre attack, putting one opponent to sleep for a few turns. What's game-breaking about it is when it is powered up by two of Elegost's Passive Skills: Sleep Volley and Lingering Sleep. The first makes Arrows of Sleep hit all enemies; the second makes the sleep last forever (or at least until they are hit with something). Most Bosses and a few Elite Mooks are immune to Sleep, but being able to put all the Mooks out of commission with a single hit is pretty damn powerful.
Eaoden's final passive skill, Absorb Malice, makes him immune to all spirit attacks and gives him action points every time he is hit by one. And since Sauron only has spirit powers, all he can do is enable Eaoden to spam his most powerful attacks without worrying about action points.
Morwen is a bit short on the game breaker department, at least compared to the other characters. But she has one in her Thief Craft tree that makes the enemy unable to target her for a few turns. With enough Speed and a way to replenish your AP, she can stay invincible.
Using Cloak of the Plains, she is the only character that can destroy the final boss single handed.
Stunning and Crippling. Most bosses are vulnerable to at least one of them, and since you can see the turn order several turns ahead, if you have any sense of planning ahead at all you can prevent some bosses from ever attacking you at all.
Fear is even worse, and it's available as a Shadowcraft through the Elfstone of Fell Shadow, meaning that everyone can learn it with enough grinding. It completely immobilizes an enemy for several turns, making them unable to doge your attacks or counter attack. And almost every single enemy in the game(except bosses of course) is vulnerable to it. There's a Lightcraft that does the same thing, but also does damage to the enemy while it's active.
The Elfstones of Fell Shadow and Pure Light are game breakers too. They are able to teach any character skills such as healing, AP draining, hasting, resurrection, slowing opponent's attacks, stopping them from using Spirit Moves, putting them to sleep, Fear (see above) and powerful Light, Shadow, and Fire Spirit attacks. It can turn any character into a completely self-sufficient power house.
There is a certain item that can completely remove an enemies Defense stat, and no enemy in the game can defend against it. Granted, there's only four of them but it lets you reduce the time spent fighting tough bosses from half an hour upwards to less than five minutes.
Eaoden can exploit one to do way more damage than he's supposed to and leech himself to full with every attack.
Rather than gradually restore AP, Phial of Vigor will catch in a loop and spam the target character with the restoration effect at the beginning of every turn.
Hadhod's Mountain Shield blocks so much damage that it can actually render healing entirely obsolete on hard mode.
The (generally high-level) items obtained from Evil Mode can be saved onto any play file, allowing Berethor to start the game with the Sword of Isildur.
Romantic Plot Tumor: Played straight and subverted. The entirety of the game sets up this really awkward and laughably bad UST between Berethor, Idrial and Morwen when she shows up. Then right at the end the Nazgul says they have claimed what Berethor loves, right before they clash.
Berethor and Morwen had met before, actually. They were engaged, until Berethor disgraced himself by running from battle and had Laser-Guided Amnesia.
Scrappy Level: East Emnet Gullies, right after leaving Moria, is a rather confusing labyrinth of gullies and rocky promontories filled with rather tougher-than-you're-really-ready-for-at-that-point Uruk-hai. It also does practically nothing to move forward what little plot actually exists.
That One Boss: The last fight in the Helm's Deep level. Once the player moves down the stairs to aid Aragorn at the gate, they are sucked into a long (and tough) series of battles against a veritable army of Uruk-hai and, in the later stages, Trolls. The very last fight in the level is against several waves of Berserkers, who can sometimes take more than one action in a turn, and powerful Attack Trolls. Berethor's "Last Gasp" technique is more or less mandatory for this fight. Hope you restored all your HP and AP beforehand!
Defense of the Beacon. Your units are few and weak, and your lone primary hero is far from the main point that you need to defend. Meanwhile, the Witch-king is leading a sizable force of tougher evil units and, as soon as he can, starts spamming his Terror ability and preventing your units from moving at all. Good's only advantage is defensive positioning.
Charge of the Rohirrim, as well as Pelennor Fields. In both cases, your crucial heroes are lightly defended at one end of the map, while a bunch of your Elite Mooks are at the other end, with a truly massive Evil army in between. If you can't get The Cavalry into the fight quickly enough to save your leadership, you are screwed.
For the side of Evil:
Oddly enough, the very first level right after the tutorial, Mission From Rivendell. The Good forces are composed entirely of a primary hero, two secondary heroes and a large number of Elven swordsmen and archers. Meanwhile, outside of heroes, Evil has a numerically and positionally inferior force of generic Morannon Orcs.
The two missions in Isengard. Ents are bad enough on their own ... now try facing dozens at once.