This contemporary piece captures a sentimental tone, as suggested by its subtitle 'First Kiss'. Its structural approach remains within the bounds of a romantic character piece despite its modern origin.
The primary challenge is to sustain a gentle, romantic atmosphere without succumbing to excessive sentimentalism.
Comparable difficulty and character — good candidates for what to learn next.
Ballada D major 'Pierwszy pocałunek' is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 5.
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 Ballada D major 'Pierwszy pocałunek' lasts about 4 minutes.
Ballada D major 'Pierwszy pocałunek' 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 Berceuse sur le nom de Gabriel Fauré, M.74 by Maurice Ravel, Berceuse sur le nom de Gabriel Fauré by Maurice Ravel, Berceuse by Rudolf Friml — see the full similar-pieces list on this page.