nice to see this up and stickied in these forums :)

I've seen this recently, but what does it even change about the game?

If I have GOG's version of Freespace 2 already running, what do I get on top of that by installing Freespace 2 Open?

much, much better graphics, sound, and lighting

better compatibility with modern OSs and input devices

mods - including FSport which ports FS1 to the FSO engine

you can also choose to play with the older game assets for the classic look in the new engine

Oh.

Well, I guess I'm not interested in any of that, because my gamepad already works with FS2 on my machine.

There are also total conversion mods - like BSG and Wing Commander games that work in the FSO and offer something different from Freespace-stlye combat if that's what you're looking for.

As he said earlier, Freespace 2 SCP or Freespace 2 Open, allow you to get an up to date visual. It adds also new gameplay mecanics to the Freespace 2 engine, so mods, custom campaigns and total conversion can use.

You have also, higher resolution support, where the Freespace 2 vanilla only support 1024*768 resolution. With Freespace 2 Open, you can play with whatever resolution you want and you can play also on triple screen. It adds also Track IR support (if you're interesting in head tracking).
And finally, it adds better graphics (textures, effects, ship with much much more details), supports modding and supports Linux/Mac OS X and Windows.
While the vanilla only support Windows.

Here some example of what can you expect with Freespace 2 Open:
Freespace Port (conversion of Freespace 1 into Freespace 2 SCP engine): http://www.youtube.com/watch?v=hnU4r1UJOF4

Visual upgrades for Freespace 2 campaign (video taken somewhere in 2008-2009): http://www.youtube.com/watch?v=2A34DGpyUqY

Blue Planet 2 War in Heaven Campaign:
http://www.youtube.com/watch?v=xpYQ4EJuqKU
http://www.youtube.com/watch?v=0zF3--pzFho
http://www.youtube.com/watch?v=TQ_loCiPyk8

Sample of mods:
http://www.youtube.com/watch?v=8tKceQoNrBs
http://www.youtube.com/watch?v=eUS4y6BEoAc
http://www.youtube.com/watch?v=qtsO0fRnc2U
http://www.youtube.com/watch?v=_5sSvlY8MNI
http://www.youtube.com/watch?v=CiT5oXm9t3w

Hey Guys there is a new update for the Freespace 2 Open assets, here's the update and instructions.

http://www.hard-light.net/forums/index.php?topic=86475.0

Have Fun

Since the engine is open, why doesn't GOG sell the Linux version of the game?

EDIT

With FS2 once again on sale at GOG don't forget to upgrade it to Freespace 2 Open and see how good the game looks these days

http://www.fsoinstaller.com/

Freespace 2 Open rocks... upgraded graphics and a ton of new campaigns like Blueplanet

https://c2.staticflickr.com/4/3934/15416627820_d64f769e2b_c.jpg

For the life of me I cannot get that installer to run. I mean it runs, but it says it cannot find the server to download FSO. I've installed Java (against my better judgement) etc and have F'd around for almost 2 hours! This is NOT how i wanted to spend my evening. Any idea if this thing still works?

Oh, it definitely still works. According to the mirror monitor, at least 2/3 mirrors for 3.7.4 RC2 are available for all files. Perhaps you tried at a bad time, or are having connectivity issues with those servers in particular?