What is the greatest mod and why?

Short of the fact that I can neither handle a Millenium Falcon nor construct a Death Star, I love Star Wars: Requiem.  Playing this has brought me a few hours of insane pleasure.  The Star Trek mod didn't really do it for me by comparison.  I assume there must be at least one more mod that could drive me to waste more minutes of my life out there.  What are they in your opinion?