Freespace, more specifically FS2, aims at recreating World War 2 style air combat (I'm going to say Pacific Theater specifically) in space.
The cap ships are large, and have an unbelievable amount of firepower on even the smaller corvettes. Flying close to one is often times suicide.
There is no real comparison to Freespace and Freelancer. Don't let the FS title deceive you. This is not an "open" game.

First : elite
Second : Freespace
Third : privateer
4th : Wing commander series

FreeSpace is much better. Also, it's linearity makes sense. You are in the military fulfilling missions for your commanding officers.
FreeSpace 1 is a must play. The final level is possible the most awesome level in any game ever created.

DS1 wasn't bad, I think it was trying a little too hard to be Freelancer, honestly. The other problem, I found, was that you had only one ship. Sure, that ship could be upgraded a lot, but part of the joy in games like Freelancer and such was saving up to buy that new fighter you've had your eye on, and in DS1, that was sadly absent.

Oddly enough that's my reason for including it in my "Games you could never finish" thread :)
The only thing Freespace and Freelancer have in common is "FREE". One is a pretty, limited, Elite and the other is Strike Commander in space :)
I love them both :)
I just want to pimp the AI in Freespace also. Before I played Freespace I was big into Tie Fighter, X-wing, Wing Commander, X-Wing Alliance and what not... In those games you racked up 90% of all mission kills. In Freespace (and Starlancer) you have to haul ass to get kills. I've never got past Lt Commander or Double ace in Freespace 1.
However I think I perfer Starlancer but I very very slim margin. I think it had even more atmosphere than Freespace. I especially loved the first time I played and made a right royal cock-up of the first mission and the in-game communications said something about being useless but you could still go to the next mission. I replayed however and the com said something like "I heard you rookies ran into trouble" "Nothing we couldn't handle" and the the freighter - "Rookies? You could have fooled me." I love the little bits of immersion like that. Also when the Tech Computer changed from "New rookie unit" to "Uber 1337 bastards who kick serious booty."
However Freespace/Freespace 2 are only slightly behind because they rock my gaming world. If it wasn't against God and Nature (and Gender) I'd happily bear Freespace's bastard children.
Karl
Ps: Freelancer is a great deal of fun also :)
Ps: As is X3: Reunion but you need a lot of patience.
Ps: Less of a Darkstar One fan. I liked it and enjoyed it but I could just feel the potential and the greatness it could have had.

Absolutely. No questions asked.
Karl

Karlallen: I almost completely agree with you except for the order you rated Starlancer and Freespace. All those things you loved about Starlancer - I loved them too! I just wish I could finish the thing :( but for me Freelancer has the edge (just). Though when you through TIE Fighter into the mix it gets harder to choose.