The good campaign in BFME features several diversions from the movies, in that Gandalf survives Moria (and kicks the balrog's ass), and it's possible to save Boromir in Amon Hen. Thus, the player can get to see what might have happened had the two continued on in the story. For fans of Boromir (and those who loved Sean Bean's portrayal of him), it's an awesome experience to see him fighting at Helm's Deep, Minas Tirith, and even the Black Gates.
Controlling Sauron whenever he appears. He's slow, but insanely powerful, with incredibly high hit points (only summonable dragons have more), and can obliterate anyone and ANYTHING in his path. Galadriel certainly qualifies too, compared to Sauron she's more of a glass-cannon. She has faster attacks but less health.
Think that's overpowered? As of the latest updates, the Ring Heroes take the carefully developed balance that otherwise exists in the game and throws it right out of the fucking window. Galadriel can now summon Eagles, mass heal heroes, summon a meteor storm of light, and create a massive tornado that lasts for a long time and wipes the floor with anything caught in its path. And Sauron, dear God. To put this into perspective, a single Rain of Fire and a single Balrog are max-tier Mordor powers that generally mean Game Over unless the enemy has an astronomical defense set up or the Mordor seriously fucks up. Sauron can summon THREE Rain of Fire storms and TWO Balrogs. AT ONCE. Oh, and he gets the same Word of Power that Gandalf has that completely and utterly fucks up everything in a 20 mile radius. There's a reason why Ring Heroes are disabled in competitive play.
The two dwarven missions set in Laketown and Erebor, respectively. Fans of The Hobbit will enjoy seeing the dwarves and men of Dale standing side by side against the hordes of Mordor. The missions excellently convey a sense of desperation and sheer grit the dwarves and men of Dale have in their defense. If you play your cards right, you won't need the elves to be the Big Damn Heroes in the penultimate mission. Even better is the fact that King Dain canonically dies in the Tolkien universe, but survives the battle here.
Laketown in particular starts out screaming awesome. You start with King Dain and a small team of Dwarven Guardians, then you advance through Laketown finding other dwarven troops and the men of Dale to increase your forces, all while flaming boulders and buildings explode around you and water splashes across the field of battle. Then you turn the tables on Mordor and demolish their base camp, fighting through the best Mordor can throw at you in the process.