Second Life is the leading 3D virtual world. It's a space where you can be whoever you'd like, build and sell whatever you can imagine, and have fun with others from all over the globe while you explore unique virtual environments, listen to live music performances, play games, shop in the world's largest user-generated virtual goods economy, and much more.
I have been using Second Life for YEARS, and I love it. I tried IMVU once and it wasn't all that I hoped it would be. The biggest differences that did it for me were that I could walk around and the graphics. You can fly in Second life, run, jump, do gymnastics, ski, jetski, walk, etc. You can be anything from a human to an animal, and the graphics are just amazing.
The only down falls of the game are the slowness, from all the users, and the perverts or non friendly people. I don't go on websites to be a porn star, so I don't want guys messaging me asking me to bang every five seconds, and I find it hard to make friends on here. I do have quite a few friends, but it took me a long time to make them.
The only things I would change is that you can be invisible and online if you would like to be, like if you would like to shop, or build, without anyone interrupting you...you could. it would be nice if we had more user friendly players on the game. I love the friends I have, but I have seen a lot of people who are in a club and yell at people for talking in the chat box itself. And the last change I would make is to stop the lagging, the booting, and the days where you're just a white cloud.
I know they are working on a lot of these issues, and in all virtual reality games it is the best one I have seen. You can be anything and do anything. Start a career, start a talk show, DJ, be a surgeon, be a dog, etc. It's just incredible that there is a place like this.