SecondLife is a huge 3D immersive virtual world that is completely and continually built by the users themselves. It's less a 'game' than a social space that you can explore in and meet up with others in. It's so wonderful to fly around and see what's been built...and everything is interactive. It's like a shared dreamworld.
You get to create your own avatar (there are simple guidelines in the orientation and it's really intuitive and doesn't require any previous 3d skills)...so I tried to make mine look a little like me...you change the face shape, the hair, the body etc...dress it and go! Then the avatar is you and you explore this place. It's reaaaally amazing. If your system can handle it, I'd recommend you check it out yourself- there's a free trial.Here's their FAQ page (http://secondlife.com/faq.php)