The D6 system is just what the doctor ordered when you have that movie or book-inspired campaign idea, and want to get it off the ground quickly.
Not exactly essential, but a good resource none theless, especially if used creatively.
For example, I used the riverboat map as a luxury space liner in a D6 Space heist-style adventure.
A good resource for space campaigns. I'd almost call it essential, since it expands on and revises the ship building rules in D6 Space.
I was looking for some thing more Firefly/Cowboy Bebop, than BraveStarr. Your mileage may vary.