not sure how most other LotR fans like the concept of "alternate endings" in their games (most reviews of Lord of the Rings Conquest knocked the game for having an Evil side alternate ending), but i did have an interesting concept for a Lord of the Rings-based game.
you play as Aragorn, starting with him as a young man shortly before his mother dies. then you get to kind of "free roam" throughout Middle Earth, hunting orcs with the Sons of Elrond, keeping Eriador safe with the Rangers, fighting in wars with Gondor and Rohan, traveling to Lorien, Harad, etc. interacting with Gandalf, Elrond, many significant characters from the lore (and new ones as well)
then the "endgame", or the main quest as it were, starts with Gandalf sending you on a little errand to find Gollum. seems simple enough, right? WRONG! you have to chase him everywhere, even to the borders of Mordor, then finally you capture him and have to take him back to Mirkwood, all the while he tries to escape and fights with you. then you go back to your side-quests and orc-hunting, then suddenly Gandalf sends you back to Bree (which at this point is kind of a hub in central Eriador) to guide some Half-ling friends of his to Rivendell.
the rest goes as one might expect, but with a twist. throughout the "bulk" of the story, you are around people who tell you about the history of Men and you get to experience their cultures firsthand. this will then drive your choice, which will also decide how the game ends. you can choose to follow the right path and become King of Gondor and Arnor (which should be difficult to achieve, though obviously more rewarding for it being the "right" ending), or just win the war as a "chieftain of the Rangers" and disappear back into the North. or you can let everyone down, try to take the Ring and claim mastery over it. granted this would make the game MUCH harder, as most of your allies would now forsake you and Sauron would throw everything at you (if he hasn't already taken the Ring from you one way or another), but you might, if you're lucky, get to beat Sauron quicker and get the "tyrannical" ending