Playing the game from the disc only was terrible. It couldn't pick up pitches correctly and seemed to have a terrible echo. It was done in the PS2 fashion, so no customizable characters etc. Having played the PS2 version originally, it is exactly like that version of RockBand. Since you buy the game and then download, they simply wrote the disc version in PS2 format only to save money, the DLC is PS3 quality.
Now if you download it, it is all fantastic! Only downside is I was hoping we would get more country outfits!