I won't bother reviewing Firefly itself because you're all shiny enough to know what's happening in the 'verse, instead I'll concentrate on the Blu-Ray factor.
This IS a better release than the DVDs, no question. The scenes that were filmed look definitively high definition and show details such as fabric weaves and monitor displays. The low light areas are also much improved and the detail is more obvious. Some scenes, primarily SFX clips, were not created with HD in mind and remain stubbornly standard definition. To my surprise this is not as grating as I'd expected. I run a 52" 1080 TV and therefore I'd presumed the SD clips would stand out like the proverbial sore thumb but no ... they integrate quite well. Bear in mind that even the SD clips will look slightly better on Blu-Ray because DVD is not quite broadcast resolution and so Blu-Ray can add those extra few lines that the DVD was missing.
The audio is very good. The DTS Master track sounds great and really reveals the subtlety in the string driven music that accompanies the series. The surround efficiency has been improved to with the 3D soundscape seeming much more coherent.
As I said, I'm surprised by how much I like this Blu-Ray release and for any Firefly appreciator with a reasonably good HD system then don't even think about not buying it!
Oh, nice menus too.

This is THE greatest show in the history of television.
Now just as a forewarning, I am very biased. I'm a Browncoat till I die!
The first time I ever came into contact with the Firefly universe, was way back when the movie "Serenity" was released. I usually read my local papers on Friday's for the movie reviews. I saw a movie called "Serenity" that got a full 4 out of 4 stars from Lawrence Toppmann. This was a big surprise, because I had never heard of it until then! Unfortunately it wasn't showing in my local theater, so I waited for the DVD. I was instantly hooked.
The Firefly universe is so lively and interesting that you can't help but want to be a part of it in someway.
After seeing the movie I of course set out for the shows. I bought Firefly on DVD. I could not believe how brilliant this show was and that it only lasted 1 season. But that one season was enough to make me a fanatic.
Now, here we have the complete series on Blu-Ray. Watching the original shows on DVD on my dad's DVD player was amazing as it is, what with the upscaling and all. But the Blu-Ray is even more amazing to watch. It just brings you that much closer to the universe. A great buy!
If you haven't already enjoyed the wonders of the Firefly universe, do yourself a favor and pick this up! If you can't afford the price of the Blu-Ray, then by all means, get the standard DVDs! You won't be disappointed.

this set gets me excited for the movie in blu-ray. great tv show great picture!

Beatiful set; even the menu option is gorgeous. The new commentary on "Our Mrs. Reynolds" and the reunion brunch with Joss Whedon, Nathan Fillion, Alan Tudyk, and Ron Glass should be enough for any Browncoat to make this purchase.

I've watched my old FIREFLY series so many times I'm surprised they still play. I love this show! I wasn't expecting much from the BLU RAY disc, after all, this program was filmed in 2002. Well guess what..... this new disc is awesome!! The color and clarity make you feel like you are watching it for the first time. I'm actually seeing things in some scenes that I barely noticed before. This Blu ray is just an outstanding example of making a great show even better.