I got it during the big Mongoose writing hiring craze. Honestly, it didn't wow me. Like others have said, I could tell that Mongoose was trying to stay true to the series, and that's good, but my gut feeling never got past "This didn't need its own system." It could have been perfectly good as a d20 Modern book, with the OGL for character creation or something along those lines. (Don't have books with me, so it's possible that B5 came out before d20M, which would explain some of it.)
Liked much of the ship-to-ship stuff, however, and enjoyed some of the underlying ideas, as well as the season guide with "how to make a game out of this episode" stuff. That was excellent.