"Mass Effect isn't plural (we wouldn't say "Mass Effects"). Instead it's a single phenomenon that you would use like "gravity" or "heat." So we also wouldn't say 'What's a Mass Effect' -- it would be 'What is mass effect?' Again, its use is like the term 'gravity,' where you would say 'what's gravity?' instead of 'what's a gravity?'"
Got that? Good. The plot of Mass Effect revolves around newly-discovered mass effect that some people can control and gives them telekinetic powers. Sounds a bit like the Force, doesn't it? Don't tell that to Hudson, who denies any similarities to the Star Wars mystical energy. While it is true that mass effect is a phenomenon and the Force is derived from internal midi-chlorians, the end-result is strikingly similar. Still, we're convinced that BioWare can make a great Star Wars-esque game.
Mass Effect should be out on the Xbox 360 in April 2007. Just be careful how you use it in a sentence.
Video of E3 Mass Effect demo hits XBLM