I just finished the book also... My Own Kind of Freedom, and it's wonderful, just as Steve said. I watched the series first (only around 15 episodes, so it's not a herculean task).
The impression I got was that it was almost like reading a movie script. (Wouldn't that be nice - a movie based on the book!) But wow, it was good if you are a FireFly fan.
I would gladly buy a second Firefly book if he wrote one. Well worth reading and just a lot of fun.
Now I'm on to watching the Serenity movie. And then, just like the first time I finished the FireFly shows, I'll sadly say good-bye to the crew until I forget enough to start all over.