Well, not for nothing what you're asking is almost like asking someone to describe all of star trek for you in a 20 second ad. It really can't be done (which is why few star trek ads do more than what was shown in the trailer above). There are many themes covered in the game, ranging from "what is life" to "how far will you go to save you're species". Mass Effect covers multiple plot threads that spans (easily) over 100 hours of play time, with outcomes changing depending on YOUR choice.I clicked on the link and found this:
That sounds about as exciting as George Lucas' blather about taxes and trade routes. Of course, Game of Thrones might sound like that, too, if summarized into a boring generic paragraph, so I'm still trying to figure out if there's a story here on par with what Game of Thrones has been delivering, or even the potential of one being created.The Krogan Rebellions were a major conflict between the krogan and the Citadel Council that began in 700 CE and continued for decades. The Rebellions were preceded by over three hundred years of aggressive krogan expansion coupled with booming population growth. Tensions came to a head when the krogan remorselessly advanced onto worlds already claimed by other races. With the krogan unwilling to back down despite Council demands, the Rebellions ensued.
I'm still waiting for someone to step up and take the role of showrunner/advocate, who has cornered a SyFy exec in the elevator between taking pitches for Vampire Paramedic and Teenage Mutant Werewolf PI. Help us Obi-Wan Kenobi! If your pitch doesn't succeed, we'll just get more of that dreck. How do you change the soulless suit's mind in 20 seconds or less?
Trying to get a shmuck on the internet who isn't trained in marketing to develop a pitch that can convince a TV exec is a hopeless cause

http://www.youtube.com/watch?v=eBktyyaV9LY&oref=http%3A%2F%2Fwww.youtube.com%2Fresults%3Fsearch_query%3Dtake%2Bearth%2Bback%26oq%3Dtake%2Bearth%2Bback%26aq%3Df%26aqi%3Dg10%26aql%3D%26gs_l%3Dyoutube.3..0l10.606l2367l0l2545l15l15l0l9l9l0l97l458l6l6l0.
Is that really all that different from this DS9 teaser?
http://www.youtube.com/watch?v=QM_uPsLONnk