The book had a lot of problems with regards to rules- I didn't try, but I had two VERY smart people in my group spend hours trying to build a ship and figure out how to run it because of how many errors there were in the book, and how confusing it tended to be. There's been no errata issued for a large number of problems. Space combat left us all scratching our heads, and saying "screw it" after we tried un-succesfully once.
The content was pretty cool, and it had lots of fun fluff- but I found the system sort of lacking... too freeform, and the idea of plot points requires a VERY good DM to do correctly. For instance, a pilot might fly the ship for the entire session- but never get a plot point because flying the ship is sort of assumed, while the guy who does the shooting will get plot points.
I also didn't like the idea that there were not static bonuses- and everything relied on very random dice rolls. In D&D- a +10 is a +10, even if you roll a 1 on a check. In serenity- I can be damn good at something (d12+d2), and spent plot points (we'll say 4 of them for a d8) and still end up with a very low roll... it got kind of irritating when my universe-reknowned surgeon couldn't diagnose a simple disease cause of a bad roll...
Also, I heard that universal stepped in and said they couldn't market anymore products or supplements for the system starting 2007. So what you have is what you get.
I personally loved Serenity- but the system didn't really do it for me. Just my two cents.
Vorp
Edit: And I hated advancement- the idea I could only improve ONE thing per session got really old... especially when I just wanted to add a d2 to something.