Theodore Oesten's 'Bluettes de l'opéra' are brilliant fantasias on operatic themes, designed for the virtuoso pianist. They are characterized by their showy runs, dazzling figurations, and dramatic flair.
Requires significant finger strength and agility for the rapid, virtuosic passages.
Bluettes is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 4.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Bluettes lasts about 4 minutes.
Bluettes is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.