for what it's worth, spaceforce: rogue galaxy was an excellent game, despite the mediocre metacritic rating. it's 30 bucks on steam atm, last time i noticed.
edit: i should point out, if for some reason you didn't like x3 (which was space sim gold, after you got the hang of it), then you might have issues with spaceforce since the story is...not really there. well, in a relative sense. it's got a steep learning curve, too.