It does not have a grade because it is too advanced. It's bad to put a grade on everything, you know.

I have not heard the piece, but knowing Liszt transcriptions, the piano writing is going to incredibly ingenius and also incredibly difficult.
Have you even heard the original? (People in this forum should remember that orchestras do exist, but they don't exist only to accompany your playing of Rach 3

) It's recommended that you listen to the original first, as listening to an orchestral work that is regarded as one of Beethoven's finest on the piano would cause many people to want to burn your house down.

BTW, the first four notes of the first movement is what some people call "Fate knocks at the door". Fate will knock at your door if you don't give the original a listen.
