Bilirubina is a contemporary work that utilizes modern harmonic language and percussive piano writing. It is characterized by its rhythmic vitality and sharp, angular motivic development.
The piece requires a high level of speed and agility, alongside crisp articulation to emphasize the modernist, angular themes.
Comparable difficulty and character — good candidates for what to learn next.
Bilirubina is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
Bilirubina is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Alexander's Ragtime Band by Irving Berlin, 'S Wonderful by George Gershwin, Rondo capriccioso in E major by Felix Mendelssohn — see the full similar-pieces list on this page.