Shepard repeated the introductions for Eragon's benefit, and then reponded to Sherman's question.
"Well I'm from Earth just as you are, though of course I was born several hundred years after you. Things on Earth alone are very different. The planet is covered in vast cities, greater than any you've seen in this world. There aren't any completely natural areas like this any more. On the flip side, humans live much longer. We've eradicated a lot of diseases that were rampant in your day. We also have easily mass produced food, and of course space travel, so starvation and overcrowding are not as big a problem as before.
Off the planet, well, you wouldn't believe it without seeing it. We've colonised quite a few worlds, and formed alliances with a number of alien races. Some of the world's inhabited by them, or us, are just small frontier facilities. Others are dazzling cities that eclipse even those of Earth. The Council that I work for govern these races. You've already seen Garrus. He's a turian, and a member of one of the council races, there are three others besides humans. Thane and Grunt are drell and krogan respectively. They don't have Council representatives, but tend to stick to their own worlds." Her mood darkened slightly.
"Of course, the galaxy is no Utopia. There are pirates, hostile worlds, the Geth, a race of synthetic humanoids created by Tali's race, the Quarians, who then turned on their creators and almost wiped them out. And then there's the Reapers. An ancient race of living starships, completely enigmatic, and destructive. They've wiped out all intelligent life in the past, and are preparing to do it again, unless we can stop them."
OOC: Phew, that was long. Still, I think it sums up the Mass Effect galaxy nicely.