You'll definitely want to try Star Ocean: Till the End of Time. Star Ocean: The Second Story is great too, just beware the horrible voice acting...and of course, watch out for the remake of the first two Star Oceans on the PSP.

A little thing though, although all of the SO games have science-fiction backgrounds, much of the games take place on an underdeveloped planet, which gives them more of a fantasy feel for a good portion of the story. But there's still plenty of sci-fi, since they all borrow heavily from Star Trek.

As for a more heavily sci-fi themed RPG, I would definitely recommend Rogue Galaxy.