Rock Band has not yet been released for the Playstation 2 although recent reports have found out that when it does, it will be a much watered down version of the game.
Obviously, the game is not going to support any online play as well as downloadable content, unlike the PS3 and Xbox 360 versions. Some things that were a little less expected are the fact that the World Tour mode is going to much different in the sense that it is very linear as well as the fact that you will not be able to customize characters or gain cash and fans.
Personally I feel like these features are the some of the main differences that caused the game to stand apart from Guitar Hero. Without them, I don’t really feel like the game is worth purchasing.
Hopefully Harmonix and MTV will at least be able to release expansion patches for PS2 owners so that they can get new songs because I’ve already played through them all on my 360 version and if I knew that there were no more songs, I would be pretty pissed.