I have a few ideas on how to improve Mordor.
1. Orodruin Biome - I already did a post on this one, so I won't go into detail on it.
2. Barad-dur Terrain - I was thinking much like how you can make hills that always spawn in one place, you can make a sort of crater at Barad-dur. This crater would extend pretty far out, but it would be such a gradual decline, that it wouldn't even be noticable. I think this crater should go down to almost bedrock level. That way, players who want to build Barad-dur are less affected by the height limit.
3. Negative Mordor-Aligned Player Receive Special Effect - I'm thinking that players who have a negative Mordor alignment should receive some sort of nausea effect. In the books, Tolkien really emphasizes the sort of tiring and mentally-exhausting effects that being in Mordor can have on a person (or a Hobbit).