Aside from the graphical issues and repetetive side missions this is a great game with a great story.
On the positive side, Mass effect combines a compelling story, that ranges from action to love drama, with a sense of you telling the story yourself. When playing solely through the main quest there will never be a dull moment. Bioware has always done a fantastic job of keeping the player interested in the story of their games alone, and Mass Effect is no exception. You play as Commander Shepard whose back story is decided by you before the game. You can either be a ruthless soldier with questionable leading skills, or a marveled hero with high moral standards. Whichever you choose there will be no doubt that you're the man (or woman) to save the galaxy. As in KOTOR 1 and 2 throughout the game you'll have a choice system, but in Mass Effect its not as black and white. You can be the protagonist or the antagonist, but you'll never be a bad guy. In other words you can complete your missions as ruthlessly and efficiently as possible, or you can consider the moral questions certain missions pose and go about them accordingly. The story pits you against a rogue alien named Saren, which has betrayed the intergalactic council made up of collective alien races. This council is kind of like the UN of the Milky Way. Without getting into any spoilers, you go on a mission throughout the Milky Way meeting allies, fighting enemies, all the while picking up clues that eventually lead you to Saren. Oh and by the way you have a choice of having sex with two females, and one of them is an alien; can it get any better than that?
The only things that mar the great experience which is Mass Effect, are the repetitive side missions and constant texture pop-ins. If you veer away from the main story, you'll find yourself going to desolate planets doing search and destroy missions. Its always the same; you land on some God forsaken planet on the Mako (your all terrain vehicle with very bad controls) and take out the enemy forces which have control of your base, and thats about it. The textures on the characters and environments always take at least 3 seconds to appear every time the game loads, which bothers me because it messes up an otherwise beautiful looking game.
Aside from the graphical issues and repetitive side missions, Mass Effect has a wide range of interactive story telling that never gets boring.