Well, I brought it for mostly alone play but I still think it was worth it.
Plus, all of the kit from RB1 is compatiable for RB2. So, you could buy the disc for RB2 later on if you run out of entertainement with RB1.
It's equal on both sides for the most part. For example the drums to RB1 are louder, though sliencing pads can be brought, where as most people just have trouble with the RB2 drums hitting random notes (they hit red rapidly, green will be hit for no reason). Other than that, I don't know of any other differences. Though I would recommend only buying the drums if you're alone, say if you don't live with your parents because they WILL get annoyed with the noise. Just let me know if there's anything else you want me to clarify :]