But what's more important, is that the game is a lot of fun. I really enjoy sneaking around the ruins and Orc strongholds of Mordor, hiding in the shadows and killing Orcs left and right. There are also some parallel story-lines, which develop the land and the various (non-hostile) characters you meet. But the true draw of the game is the ability to kill vast numbers of Orcs in the most spectacular way. As you gain more power, you get more impressive combat moves and more 'wraith' powers.
There's also the "Nemesis System", which is a really cool way to generate content. When you kill Orcs, others take their place in the hierarchy of Sauron's army. They're randomly generated, with random strengths and weaknesses. They gain power by fighting against the other captains (or killing you!), lose weaknesses and gain more power. That means that even if you don't want to (or can't) advance the story, there is always the possibility to go in and wreck some Orc party!
(It's a bit like the Radiant Quest system that was built into Skyrim to keep generating content, but after a while there was no reason to keep doing those missions: all you got was a lousy 100 gold. With this game, as captains gain more power, the missions become more difficult and the runes you gain (runes go on sword, bow and dagger to gain abilities) become more powerful as well. Better system, in my opinion.)
And then I thought: wouldn't it be cool to do this in a tabletop RPG? Have a group of PCs be the infiltrators, tracking the ranks in the enemy army, and interfering to change things to your advantage?
Something to think about.