The textures may be good, but the lighting is even better. There's a tendency to go overboard with HDR lighting in games these days, but in Mass Effect the HDR is measured and incredibly effective. Yes, you'll encounter some intense bloom, that almost whites out the screen, but most of the time the lighting just adds atmosphere, especially when it's reflecting off glass, or water.
Bioware has also thrown in some great cinematic effects. I'm particularly fond of the film grain effect, which really adds to the immersive nature of the game, although if you don't like the film grain, you can actually turn it off in the options menu. Mass Effect also sports the best depth of field effects this side of Crysis - it makes it very easy to mark out the focus of the scene, with everything else just slightly blurred.
But truly breathtaking as the visuals are, it's the story that really drives Mass Effect on. The game achieves something that so many other titles aim for, a truly epic feel. Admittedly, the basic premise could have been lifted from any number of Sci-Fi movies or TV shows, but that's not necessarily a bad thing. In fact, a degree of familiarity just makes it easier to immerse yourself in Mass Effect.
I won't go into much detail about the story, since you really want to experience it for yourself. The basic premise however, has your Commander Shepherd being recruited into the ranks of an elite galactic force known as the Spectres. Your first mission as a Spectre is to track down one of your brethren, who has turned against the order and joined forces with the Geth - a race of mechanical life forms, hell bent on destroying organic life. Battlestar Galactica anyone?
Obviously the story develops as you progress through the game, just like it would if you were watching a movie. But in Mass Effect, your actions, or inactions can drastically change where the story takes you. Under normal circumstances I would say that this kind of feature adds up to a strong chance of replay for a game, but considering that you're looking at around 25 hours of play if you shoot straight through the game in a linear manner, you'd be dedicating a large portion of your life to Mass Effect if you wanted to see all three of the endings. Add to this the fact that if you chose to explore every planet and complete every side quest, you'll be looking at a far longer playtime.