It's not a generic science fiction RPG. It models 1970s interstellar sci-fi pretty well, but if you're trying to replicate Star Trek or Star Wars, you're better off with one of the games designed around that. It does do a Firefly-style game very well, to the point that Firefly looks an awful lot like a Traveller TV show.
Even the Mongoose version shows its age -- the original game's age, that is -- but it does the job. The only issue I've run into is that there's no leveling up mechanism for players, and for some players (like most of mine) that's a deal breaker. (The game's assumptions on what kind of stuff can be found circling a star is also wildly out of date; I'm torn on whether that's a bug or a feature.)
