This game made me feel like the captain of a space ship. There was nothing like it at the time it was released, and even now I have not experienced any other game making me feel this way. I loved Fallout 3 too, but Mass Effect had something special. It was so well crafted, I listened to every dialogue of every NPC. The characters are so memorable with amazing voice acting. The Citadel is the best city in video games, felt really alive. Most sidequests add to the story instead of just padding the gameplay time.
After playing the game, I wondered how Star Wars (movies) sucked so badly, when a video game could create a much more interesting sci-fi world and story.
Unfortunately Bioware is no longer the same company.
My favourite sci-fi game of all time is Elite. Because I am old.
There was nothing like it at the time. Not even close. It was the most immersive game you could get