Liszt's B minor Ballade is a cornerstone of the repertoire, defined by its stark harmonic transitions and demonic virtuosity. It is a masterpiece of thematic transformation and extreme emotional volatility.
The primary challenge is maintaining intensity through the lengthy development sections while navigating the frequent, taxing octave passages.
Comparable difficulty and character — good candidates for what to learn next.
Ballade No.2 (S.171) 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 No.2 (S.171) lasts about 14 minutes.
Ballade No.2 (S.171) 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 Mephisto Waltz No. 1 by Franz Liszt, Après une lecture de Dante by Franz Liszt, Cadenza to the first movement of Beethoven's Concerto No.3 by Franz Liszt — see the full similar-pieces list on this page.