This one is quite possibly one of the best Sci-Fi shooters ever. It has an incrediby compelling single player campaign that really keeps you wondering what will happen next. I would recommend also buying Freespace 1 & playing it all the way through first, though, in order to become more familiar with the plot line.
I also have the original CD, so I found it nice when GOG was offering a download that wouldn't require a CD.
Be advised; however, that the GOG version was somewhat modified from the original CD version in that there is no longer a basic setup utility (i.e.; there is no utility to allow you to set up screen resolutions, choose between OpenGL or Direct3D, etc). Because of this, it doesn't run very well on my aging Athlon XP 3200+ PC with 2 GB of memory and a 512 MB AGP GeForce 7950 GT. At the time of the original CD-ROM title release, I was running this with a much older 500 MHz K6-2 desktop and a GeForce2 card, and it ran far better.
Either way, I must give this five stars--for many of you with much newer computers, this game should run flawlessly. I just need to upgrade.