Mass Effect has a very engrossing sci-fi universe because it borrows so heavily from other sci-fi universes such as Wars, Trek, B5, BSG and others. The Geth are Cylons/Borg, the Krogans are Klingons, the Citadel is Babylon 5, Biotics are Jedi, the Terminous Systems are the Outer Rim territories... and so on. They did a great job stitching it all together into its own universe, but there's very little fresh or original to it.
Except in terms of gameplay, that is where Mass Effect excels. The action is fairly standard for a shooter, but the dialogue mechanic is fantastic, and your ability to stamp a personality onto Commander Sheppard is beyond any other game I know. It's the finest RPG I've played, this is the only game I've ever played where each replay has felt different due to playing as different characters. And unlike a lot of games, you get connected to the other characters on your team, and you know that it's your choices that determine whether they live or die.
Remove the gameplay and what you have isn't anything all that special. A Mass Effect movie could be as big as Star Wars but only if it is well written, has great characters and has superb production, but if its rests on the laurels of its universe then it's just going to be a very average science fiction movie.