If you feel like playing with much better graphics, you might want to try out the MediaVPs mod. It's basically the same as retail FS2, but with much better models, effects and backgrounds.
If you want to play the game in a chronological order, there's Freespace Port - it's the FS1 campaign ported to Freespace Open, and Freespace Port MediaVPs adds more bells and whistles to it, be sure to install and launch it too!
The next ones in chronological order are: Silent Threat Reborn (the original Silent Threat is too bad to even mention) and then FS2. After that, it's all up to you - try some mods out!
Both the Freespace 1 and Freespace 2 campaigns have got a simple yet informative couple missions long tutorial at the beginning, you might want to use these.