The 'Heroic' Polonaise is one of Chopin's most celebrated works, serving as a powerful symbol of Polish national identity. It is characterized by its bold, orchestral textures and triumphant, surging energy.
The most difficult technical hurdle is the famous left-hand octave run in the middle section, which requires both speed and stamina.
Comparable difficulty and character — good candidates for what to learn next.
Polonaise in A-flat major (Op. 53) 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 Polonaise in A-flat major (Op. 53) lasts about 7 minutes.
Polonaise in A-flat major (Op. 53) 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 Allegro de concert by Frédéric Chopin, Ballade No.2 by Frédéric Chopin, Ballade No.1 by Frédéric Chopin — see the full similar-pieces list on this page.