It's about as difficult as Fantasie Impromptu... some random fast passagework, and big-ass leaps/chords on the last page.
The one difficult part (for me at least), is on the second page, when it builds up, the left hand has these REALLY nasty broken chords downwards. They are fast, and cover much more than an octave. I think compared to his other preludes, that one section is pretty freaking tough, but overall it's one of the easier preludes..