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.
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.
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.