This early work by Alban Berg explores complex harmonic density and late-Romantic chromaticism. It demonstrates the transition from traditional variation form toward the composer's eventual atonal language.
Maintaining clarity of voice leading within a thick, dissonant harmonic texture is the main technical hurdle.
Comparable difficulty and character — good candidates for what to learn next.
12 Variationen uber en eigenes thema (1908) 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 12 Variationen uber en eigenes thema (1908) lasts about 6 minutes.
12 Variationen uber en eigenes thema (1908) 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 12 Variationen über ein eigenes Thema by Alban Berg, 12 Variationen uber en eigenes thema by Alban Berg, Ballade en mode phrygien, JA 9 by Jehan Alain — see the full similar-pieces list on this page.