Zientarski's work follows the traditional form of the lullaby with a focus on melodic clarity and balance. It reflects the Polish conservatory tradition of the late 19th century.
Pay close attention to finger-legato in the melody to ensure a seamless vocal-like quality.
Comparable difficulty and character — good candidates for what to learn next.
Berceuse (Op.43) is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 5.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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 Berceuse (Op.43) lasts about 3 minutes.
Berceuse (Op.43) 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 Blau Veilchen by Richard Eilenberg, Berceuse by Léon Boëllmann, Berceuse by Anton Simon — see the full similar-pieces list on this page.