Yesterday I signed up for Google Lively. It reminds me a lot of the early (not the current!) Twinity beta, where the environment consisted of just a bunch of room, without a real world to access. Lively is the same; it's dressed up 3D chatrooms. It's not an immersive environment either, because you always run in windowed mode as far as I can see.
Avatar editing is quite limited, you can't tweak your avatar as I'm used to in SL. The result is an avatar that doesn't look like me at all. Avatar movement is done by mouse, which requires you to keep the mouse button pressed down if you want to move the avatar. I think this may be quite hard on your hand muscles if you stay in Lively too long.
All in all I spent fifteen minutes in Lively, which is obviously too short for a thorough analysis. More to come later!
I've created a new room, put in some furniture. Feel free to check it out or add to it!