The still latest space sim shooter with the epic feel you would expect from anything space related. It's not really that long but the joy of dogfighting guarantees high replay value.
In short - get it.
If this already isn't the reason you are buying Freespace 2 on GOG, search the web for mods, they are plentiful and vastly improve the look and feel of the game by upping the graphics high enough to make running Freespace 2 a hard job for your PC.