Ok, I'm not an SG fan. I've watched the movie and a few episodes. Cool stuff but...I saw this book on the shelf at my local RPG store. After thumbing through it, I bought it before I even had the core book. After 150 pages into it, I was convinced that any RPG with a sourcebook like this MUST be good so I bought the core rulebook (see EclipsePhase). I've dabbled in Star Frontiers, Traveller and Transhuman Space. This RPG might make me a devoted GM. I don't even want to GM anything else right now.
If you've enjoyed any sci-fi/espionage RPG but were left wanting for some truly compelling setting, buy this book. If you don't, you'll never know where it might take you.