Total War: Rise of Mordor is a conversion mod for Total War: Attila that, in its final form, will let you play through a newly-crafted campaign featuring 19 factions from Middle Earth. You can take your first peek at it now thanks to a public alpha released this week that will hand you control over some of the factions and let you play around with custom units that are based on the ones you'll have seen in the films.
The background story of the campaign will be "accurate to the books", but could still be a while off yet. First, the team will finish off the factions and add custom settlements into the mod.
The grand strategy and large-scale battles of the Total War series make it ripe for Lord of the Rings conversions, and Rise of Mordor isn't the first to attempt it. Third Age does something similar for Medieval 2: Total War, and it does it very well (making it onto Tom's list of essential Total War mods a while back). But that game is more than 10 years old now, so I'm curious to see if working on a newer title like Attila will help create something better.
You can download the alpha of Rise of Mordor from its ModDB page.