I had the game for about a year without really playing it -but then when I decided to give it another shot I got hooked!
but I bought Mass Effect because of all the great things I heard about it, the immersive world, the characters, the choices and the biotic and tech powers.
I won't give away all the important plot points, because if you haven't played it yet, it would just ruin your experience. in the story you are commander Shepard (either male or female) you have to choose if you want to use guns, biotics or tech powers (I would recommend not choosing the soldier because the biotic and tech powers are so much more epic and awesome and the only real weak point in the game is the shooting mechanics.
A spectre named Saren goes rogue and it is you job to stop him and save the galaxy, to do that you have to assemble a team to help you.
In the game you can choose to be paragon or renegade (good or bad-ass), and later I found out that the consequences of you choises are carried through to the second game in the series.
all-in-all the main story-line is AWESOME!
the graphics are good, but sometimes when you load a game the textures load a bit slow, and the framerate can drop when the action is most tense.
the gameplay is awesome as long as you don't rely only on your guns, some complain about the Mako (a vehicle in the game) but I seem to be the only one in the world who disagree.
the sound is really great - and the soundtrack is EPIC and AWESOME!
I don't know if I will play it again unless they make some of the weaker points better in some sort of a remake, because now I have Mass Effect 2 which really don't have many weak points.
all in all this and amazing game with a really cool setting, story and universe that could really give both Star Wars, Star Trek and others a run for their money :D