Zhelobinsky’s Mourning Song is a poignant, technically demanding study that explores the dark resonance of the keyboard. It is distinguished by its heavy use of chromaticism and expressive dissonance.
The main challenge is maintaining a deep, resonant tone throughout the complex, chromatic inner voices.
Comparable difficulty and character — good candidates for what to learn next.
"Mourning Song" Op. 27, No. 7(bis) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 6.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 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 "Mourning Song" Op. 27, No. 7(bis) lasts about 4 minutes.
"Mourning Song" Op. 27, No. 7(bis) 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 Piano Sonata No. 14 'Moonlight', No. 2 by Ludwig van Beethoven, Nocturne in C-sharp minor by Frédéric Chopin, Body and Soul by Johnny Green — see the full similar-pieces list on this page.