This piece follows the tradition of the 19th-century 'rêverie', aiming to evoke a dreamlike state through simple harmonies and flowing melodies. It is representative of the pedagogical and amateur-focused music market of its time.
Students must pay attention to the gentle phrasing and sustaining the long melodic lines.
Comparable difficulty and character — good candidates for what to learn next.
C'était un rêve (Op.122) is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 3.
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 C'était un rêve (Op.122) lasts about 3 minutes.
C'était un rêve (Op.122) 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 Bonne nuit by Franz Hitz, Ballet des ondines by Franz Hitz, Barcarolle by Franz Hitz — see the full similar-pieces list on this page.