I was the one who mentioned Sibelius...My favourite long piano piece is Mussorgsky's Pictures at an Exhibition. He seems to stretch the instrument to the limit, much like Beethoven did in his late sonatas. I feel that the Mussorgsky is more immediately accessible, though.
Someone above has mentioned the less travelled piano works by Sibelius. To this, I would like to add Janacek's superb piano output, which includes his Sonata "From the Street, 1 October 1905" & also On the Overgrown Path.
I like that you mention Chopin pieces as a drug. I feel the same way. Hypnotic and mesmerizing. Scriabin and Rachmaninov included as well.I love almost everything by Chopin (Heroic polonaise is one of my drugs), Schumann and Mozart. I also liked Liszt and Schubert stuff, but I still don't know them as good as I should, so I can't say which works are my favorite. So far, I loved Schubert's piano trios.