Basically its an online game provider that you pay monthly for but provides hundreds if not thousands of titles on demand. The titles range from Pong all the way to Splinter Cell and Beyond Good and Evil. While small games can be downloaded instantly, large games will be downloaded in chunks and played as soon as they have the needed data.
The service will not only provide games but as much historic content covering the game that can be found. You can sit there and laugh at all those great SNES and Playstation titles.
Yes the service will LEGALLY emulate consoles, Turner got with Publishers to help them bring the games to the PC.
The system is created by Turner Broadcasting. I saw a demo of it on G4 and have been testing it for a month. It's a great Idea and I probably will sign up when it releases.
They plan to have 300 or so titles available upon opening the doors but plan to update weekly.