This is a sentimental ballad typical of late 19th-century American salon music. It is musically distinctive for its emphasis on simple, vocal-like melodic phrasing.
Students must focus on achieving a singing tone while balancing the melody against the accompaniment.
Comparable difficulty and character — good candidates for what to learn next.
'Twas but a Dream is rated Henle level 2 of 9 — beginner repertoire, roughly ABRSM grades 2–3. In the RCM system it corresponds to about level 3.
You should be comfortable at Henle level 2 — meaning you can already play level 1–2 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 'Twas but a Dream lasts about 3 minutes.
'Twas but a Dream 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 Albumblad, EG 109 by Edvard Grieg, Candlelights by Bix Beiderbecke, Billet Doux by John Stepan Zamecnik — see the full similar-pieces list on this page.