BioWare does the trick again, and Mass Effect rightfully won a place in our hearts.
Mass Effect evolves around a human commander named Shepard. In the distant future, Earth has decayed a lot, so people have made colonies in the space, together with other alien races. While Shepard serves the Citadel army, a space station built to home many different species, planet Eden Prime and the human colony there get attacked by the Geth, an AI robot race. While under attack, elite Spectre soldier Saren Arterius is seen betraying the order by killing another Spectre. Spectres are the most respected, above the law soldiers. They are not trained - they are recognized through their hard operations as normal soldiers. Shepard comes across a Prothean beacon, an extinct race who is believed to have built everything - including mass relays used for travelling through systems instantly, which grants him visions that are later revealed (not much later, just after the mission, so it's not a spoiler) to be memories of the Protheans at the time of their extinction, memories they rushed to save in the beacons so they wouldn't be lost. Later on, Shepard provides evidence of Saren's betrayal to the Council, and Saren is immediately stripped of his Spectre status and is wanted, and Shepard gets the most unexpected gift: to be the first human Spectre in history. After Shepard agrees, you're set on a mission to find Saren, who supposedly is the main antagonist, but it is later revealed that he's just a puppet of someone beyond your imagination.
The story is extremely interesting, and I avoided to provide more information so as not to spoil anything. Mass Effect is totally a guide of how-to-create-RPGs merged with shooting action that doesn't suck. (For example, Fallout 3.) Bioware once again did the trick, and with Dragon Age: Origins being the center of this year's gaming, as well with non-forgettable games like Star Wars: Knights of the Old Republic (series) or Neverwinter Nights, they show they still know how to do their job - and they can do it well. Mass Effect features deep gameplay, like a full-customizable equipment screen or player powers and talents. The graphics are really satisfying for 2007's standards, and audio gets you right into the game, especially if using a soundsystem of 4.1 or more. It actually has high replay value, since the player can make hundreds of different choices that will affect their personality as well as the world around them. Your finished save game can be imported into Mass Effect 2, and you will continue with your previous Shepard and the choices you made on the first game. For example, if a teammate gets killed on the final mission, he/she does not appear on the 2nd game but is referred to for what he/she was on the first game. Or, if you have a romantic interest in the first game, it transfers into the second game as well.