Often referred to as the 'Valse grande', this work is significantly more substantial and structurally complex than Chopin's other waltzes. It utilizes sophisticated polyrhythms and dramatic harmonic shifts to elevate the genre.
The sophisticated two-against-three and two-against-six rhythms require very secure technical grounding.
Comparable difficulty and character — good candidates for what to learn next.
Waltz in A-flat major (Op. 42) is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 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 Waltz in A-flat major (Op. 42) lasts about 7 minutes.
Waltz in A-flat major (Op. 42) 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 Fantaisie-Impromptu in C-sharp minor by Frédéric Chopin, Étude in G-flat major, No. 5 by Frédéric Chopin, Ballade No.3 by Frédéric Chopin — see the full similar-pieces list on this page.