"Neo-Impressionism" is in reference to the fact that Impressionism was a musical period. Because the classical and romantic periods are over, we now write "Neo-classical" and "Neo-romantic" music. The impressionists were around the turn of the century and led into jazz. As for what they are impressions of, I will leave that up to your imagination. Personally, the prelude reminds me of a night sky full of stars. The toccata could be anything, really. That was written more as a rhythmic and harmonic study.