Aleatory by Earl Richard Drehmer utilizes elements of indeterminate music to create an expansive, shifting soundscape. It is distinguished by its use of wide-register keyboard writing and harmonic ambiguity.
Navigating the wide-span arpeggiated figures while maintaining consistent pedaling is the essential difficulty.
Comparable difficulty and character — good candidates for what to learn next.
Aleatory is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 8.
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 Aleatory lasts about 4 minutes.
Aleatory 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 Gymnopédie No. 1 by Erik Satie, La cathédrale engloutie by Claude Debussy, Gnossienne No. 1 by Erik Satie — see the full similar-pieces list on this page.