This is a transcription/arrangement of the traditional Sicilian hymn often associated with Kreisler's violin repertoire, adapted here for piano. It features a sweeping melodic line supported by simple, lyrical harmonic accompaniment.
The primary challenge is maintaining a singing legato melody line while balancing the accompaniment to avoid overpowering the phrasing.
Comparable difficulty and character — good candidates for what to learn next.
'O Sanctissima' for High Voice & Piano is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 4.
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 'O Sanctissima' for High Voice & Piano lasts about 3 minutes.
'O Sanctissima' for High Voice & Piano 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 Black Beauty by Duke Ellington, Bright Eyes by Florence Price, Albumblatt für Clara Schumann by Johannes Brahms — see the full similar-pieces list on this page.