It is a question I’m often asked and find it quite hard to give an answer. The notion of difficulty is a subjective one, and what may seem difficult to you may seem easy to someone else. This ranking does not thus escape my subjectivity – these are the most difficult piano pieces according to me.
At the top of the pyramid, I would put Gaspard de la nuit by Maurice Ravel. Technically and musically extremely impressive, many pianists shied away from learning it.
In second place, I would put the Second Sonata by Pierre Boulez. No need to spell it out, it is an extremely difficult whole (in particular for memory) and just as Gaspard de la nuit, it fascinates me a lot, but few go through all the work required to perform it in public.
I assign the third place to the three famous movements from Petrushka by Stravinsky. Manually not so easy and musically complicated, like any other piano reduction by Stravinsky…
Some will be surprised by the fourth one: The eighth Sonata by Prokofiev.
And the last one in this very subjective ranking: the Sonata opus 106 hammerklavier by Beethoven, especially for its very famous fugue…
Let’s sum up this “top 5″:
1 – Ravel: Gaspard de la nuit
2 – Boulez : Second Sonata
3 – Stravinsky : 3 movements from Petrushka
4 – Prokofiev : Eighth Sonata
5 – Beethoven : Sonata Hammerklavier opus 106.
Of course, this is just my point of view on the subject and you will certainly hear about other suggestions elsewhere. Notice that 4 in 5 works are from the 20th century, at a time when piano technique and pianos greatly evolved.
And you, what would you add to this list? What are your criterions for considering a work to be difficult?