For example the game in PS2 has a size of 1.8 GB, while the game fits correctly in a DVD-5 for the console, that's not the case in GCN due the 1.35GB limit of the mini dvd.
So the game was split into two mini dvds, so pretty much what you have in that second disc is the second half of the game.
I think both discs has the original arcade game but with a change of music because of the copyright, but I am not sure if you can play the second disc without starting a new run in the first disc.
Game is good, it's like Turtles in Time mixed with the third game for GB but in 3D.
Edit: I sent this before I watched the last message.
First disc is like 600MB and the second one about the same.