Werner Wehrli's variations utilize a Swiss folk theme to construct a series of character pieces. The work blends classical formal structures with early 20th-century melodic charm.
The primary challenge is balancing the lyrical melody against the varied harmonic accompaniment.
Comparable difficulty and character — good candidates for what to learn next.
12 Variationen über 'Im Aargäu sind zwöi Liebi' (Op.45) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 8.
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 12 Variationen über 'Im Aargäu sind zwöi Liebi' (Op.45) lasts about 7 minutes.
12 Variationen über 'Im Aargäu sind zwöi Liebi' (Op.45) 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 Piano Sonata No. 11 in A major by Wolfgang Amadeus Mozart, Capriccio di valse by Constantin von Sternberg, The Entertainer by Scott Joplin — see the full similar-pieces list on this page.