While Middle-earth games assume the PCs are going to be good guys, I know a few people who enjoy playing evil characters. At least one MERP adventure (I forget which) allowed the PCs to take the villainous route.
I have a few MERP characters that are evil, although they work for themselves instead of Sauron. The animist is probably a priest of Sauron, however. I created them to serve as the antagonists for my main characters, who are of course heroes. I haven't played a lot of MERP recently, so this idea hasn't gone very far.
But maybe you can have a short-term campaign about villains set just before and during the War of the Ring. The PCs will be humans and half-orcs terrorizing Bree-land and the Shire under Saruman's orders. The PCs can be fighters, thieves, and assassins. They may be brigands accosting travelers or spies infiltrating the towns after the Rangers have gone to war. Their forces will eventually be routed during the Battle of Bywater, but allow the PCs a chance to escape, so they may continue their villainy somewhere else.