Alfred Grünfeld was a virtuoso pianist whose compositions are characterized by a refined, salon-style elegance. This Op. 21 work utilizes delicate ornamentation to decorate its long, lyrical melodic lines.
The primary difficulty is the seamless integration of ornamentation without disrupting the flow of the main melody.
Comparable difficulty and character — good candidates for what to learn next.
Barcarole No.1 Op.21 is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
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 Barcarole No.1 Op.21 lasts about 4 minutes.
Barcarole No.1 Op.21 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 Barcarole by Alfred Grünfeld, Barcarole No.2 Op.24 by Alfred Grünfeld, Barcarole No.3 Op.38 by Alfred Grünfeld — see the full similar-pieces list on this page.