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