Merkel was a master of the German Romantic pedagogical and salon tradition. This piece is a quintessential Barcarolle, relying on steady harmonic support and a flowing, vocal-style melody.
Focus on legato playing and maintaining an even, undulating pulse throughout.
Comparable difficulty and character — good candidates for what to learn next.
Barcarole (Op. 63) 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 Barcarole (Op. 63) lasts about 4 minutes.
Barcarole (Op. 63) 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 by Georges Bizet, Berceuse sur le nom de Gabriel Fauré, M.74 by Maurice Ravel, Berceuse sur le nom de Gabriel Fauré by Maurice Ravel — see the full similar-pieces list on this page.