Ignaz Friedman, a master pianist, composed this ballade with high virtuosic demands and a flair for improvisational-style rhetoric. It combines technical showmanship with deep, emotional intensity.
Achieving the correct rhythmic flexibility (rubato) within the fast, bravura octave passages is the primary challenge.
Comparable difficulty and character — good candidates for what to learn next.
Ballade (Op.66) is rated Henle level 8 of 9 — concert repertoire, roughly diploma level. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 8 — meaning you can already play level 7–8 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 Ballade (Op.66) lasts about 9 minutes.
Ballade (Op.66) 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 Ballade No.1 by Frederic Chopin, Ballade No.4 by Frédéric Chopin, 'Ch'io mi scordi di te?' by Wolfgang Amadeus Mozart — see the full similar-pieces list on this page.