BUY IT.
Sorry. Let me try and elaborate -
It's from the developers of Knights of the Old Republic. It's more RPG than sim, but there is a lot of real-time action in it. Unfortunately, no spaceship flying, but you do get to use this neato battle tank to explore planets with.
The story is you play a human, in a galaxy where humans are considered rather primitive, who needs to uncover the mystery of why this honorable super elite soldier went rogue, and you uncover a secret that can change the fate for all species of the galaxy. What makes this game great is the level of customization that is allowed for your character, from general appearances to the attitude you take in conversations, and the depth of interactions with all sorts of character.
The game is as close to a "sandbox" game for scifi enthusiasts as you can get, but I do find things can get a tad repetive, especially if you're trying to unlock achievements for exploring the galaxy and collecting missing pieces.
The game is pretty huge, in terms of story, level design, and voice acting (unlike KotOR, there aren't any generic alien language clips that you hear over and over again). It's also quite beautiful, and near seamless, minus some boring elevator action (
haha).
The reviews can go into greater detail, but I would definitely suggest picking it up, especially since I saw recently it's part of the $20 Platinum Choice series (or whatever XBox calls there cheap bestsellers).