IMC is a chat site for roleplaying games—designed by and for roleplayers. Here, you can participate in any of a number of existing gaming environments (“rooms”), or create your own game and play with your friends.
Yes. IMC is free to use and has no advertising, save for promotion of other rooms on IMC itself.
The main focus of IMC is people who are interested in role-playing games. The structure of the chat rooms is set up to reflect this: each room is a different world or settings.
IMC is not a general "meet-and-greet" chat site; its focus is role-playing games. It is also not a "hot tub" or sex-chat site. Even though some of the environments in IMC are labeled "M" for mature players, that does not imply that any explicit activities are taking place.
IMC is also not an MMORPG like World of Warcraft or City of Heroes. There are no 3D graphics or automated gameplay; the environment uses mainly text (and occasional static graphics) to drive the imaginations of its users.