August Eberhard Müller's Fantasia Op. 35 reflects the transitional period between the high Classical and early Romantic styles. It features expressive harmonic shifts and an idiomatic use of keyboard ornamentation.
At Henle 5 this is a late-intermediate piece — technically substantial, with musical demands to match. The main demands: ornaments that need to sound effortless, not squeezed in; a true singing tone, with the melody floating above the accompaniment; and chord voicing — bringing out one note inside a handful of others.
The main technical hurdle is integrating fluid ornamentation into the cantabile melodic lines without disrupting the pulse.
Comparable difficulty and character — good candidates for what to learn next.
A level or two down with the same spirit — ideal if this piece is still out of reach.
Where this piece's skills lead: slightly harder works making similar technical demands.
Lesser-known works by the same hand, at a comparable level.
Fantasia (Op.35) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 6.
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 Fantasia (Op.35) lasts about 5 minutes.
Fantasia (Op.35) 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 Nocturne in B-flat minor, No. 1 by Frédéric Chopin, El Cant dels Ocells by Hideo Kamioka, Berceuse élégiaque, BV 252a by Ferruccio Busoni — see the full similar-pieces list on this page.