Second Life isn't really a "game" but I think it fits here best.
Second Life is about making an avatar (your character) with wich you go around in a virtual world built mostly by other people (I mean, not by the SL administration). You can buy and sell items you build but you need Linden Dollar (L$) to buy things and these L$ cost you real money unless you earn some in Second Life (for example by dancing or sitting).
It's quite boring imo if you don't have an own place or something like that but own land costs you even a monthly fee + some extra $ if you own "big" land.
I dislike SL a lot for having this fees.
If you just want to walk around and build some stuff with standard textures or free textures etc. you don't have to pay anything.
BUT.
There are also positive things. In aspect of Jpop are to be mentioned the B.L.T. (you know, that magazine) building where they show like every cover ever published in a room. Also on the same island is the AKB48 central and a/the Tokyo Tower as well as a big building of a jap. mobile company (I think it's NTT DoCoMo). For me more interesting on some mainland: Dohhhhup's space. You have probably seen it on some older "Hobby" videos of dohhhup.com, they have a video panel there and advertise new singles of H!P. Sometimes you can have a short chat with dohhhup staff people if there is someone around.
I will probably use this thread to show you what I do in SL and stuff like that. I hope there are also other people around here who lurk in SL or want to lurk there so I don't need to spam this thread alone and maybe get some more companion in SL. If you want to know where some places are you can ask me.
For me it's mostly either like a 3D chatroom or a playground

Now, here my latest construction. The Berryz wall.

Well, the most latest is the momobot, a supposed to be Momoko-bot, script I wrote. You can talk with her and she answers sometimes randomly sometimes fixed.