Op. 33 is an expanded version of the composer's earlier droplet-themed works, featuring more complex rhythmic layering. It distinguishes itself through its increased attention to subtle dynamic shifts in the treble register.
Mastering the balance between the melodic fragments and the quiet, recurring background ostinato is essential.
Comparable difficulty and character — good candidates for what to learn next.
...before the droplet hits water (Op.33) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 6.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 ...before the droplet hits water (Op.33) lasts about 3 minutes.
...before the droplet hits water (Op.33) 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 ...before a droplet hits the water by Xavier Shuang Xu, ...before the droplet hits water by Xavier Shuang Xu, Gymnopédie No. 1 by Erik Satie — see the full similar-pieces list on this page.