Originally a song, this famous melody has become a staple of the light classical piano repertoire. Its enduring appeal lies in its infectious, sweeping melody and romantic character.
Work on the seamless integration of the melody with the left-hand waltz accompaniment.
Comparable difficulty and character — good candidates for what to learn next.
Amapola 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 Amapola lasts about 4 minutes.
Amapola 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 Waltz No. 2 by Dmitri Shostakovich, Waltz in C-sharp minor, No. 2 by Frédéric Chopin, Belle of the Ball by Leroy Anderson — see the full similar-pieces list on this page.