The easiest means of determining that is actually trying the software, in all respect, Kara.
I'd say that Starshatter lacks as in-depth a mission building environement as FreeSpace, but then again, that's because it's principally intended to be more of a dynamic combat simulation rather than a mission-based game. To counter the previous statement, the dynamic aspect of the program could be a lot better. Like FS, I believe it only runs on a single core at this time, so until the day comes about that multi-thread coding is implemented, it will suffer the same limits as FS in that regard.
Starshatter, with a good deal of work I'd assume, could effectively be transformed into a full Newtonian-flight combat sim. Right now, it's semi-newtonian at best, albeit better than FS. It posseses atmospheric flight functions for fighters, ship docking/landings, and native support for capitol ship command and control, as well as mission planning functions. Many people seem to think it is in fact an RTS; in that regard, note that Falcon 4.0 can be used as an RTS... Gameplay-wise, it's a very fascinating engine to consider working with.
Possibly of more immediate interest, Starshatter stores campaigns, mods, and missions in a compressed .dat format, and has a purpose-built mod building utility (starmod). Looking into this code may be of interest, as has been noted in other conversations, the uncompressed .mv file format has been of want for upgrade for a while now. Starshatter's .dat format might not be the best alternative, but it is at least now open source and can thus be reverse-engineered (if that proves to be a useful study).