I am a freelancer veteran, having played the game for 5 years and explored ever nook and cranny, as well as modded the crap out of the game, so i can first tell your friend that he will most likely love freespace 2. The second thing i'd tell him is that its completely different than freelancer. Freespace 2 is mission based, meaning you can't go out and do whatever you want, your dead set on a single campaign route. Surprisingly (at least, to freelancer players), this will not degrade the gaming experience. It lets freespace 2 give you a storyline experience like no other space sim has. The other important difference is that combat is waaaaay different. You still go around shooting people, you still have a targeting system (and it functions similar to freelancer's), but your in first person mode and its quite realistic, unlike Freelancer's rather fantasy version of fighting.
The third difference is that Capships are no longer celestial ornaments, they are very, very important, probably more important than you. Commanding your squadmates is almost the only way to get things done, and trying to do everything yourself, like you do in freelancer, is just going to get you killed. There's no real upgrading ships, you just get better ships as the game goes along, and all the missions are tweaked based on that.
Thats a description of freespace 2 direct from a freelancer.
Freelancer, by the way, kicks f***ing ass.
