João Domingos Bomtempo was the most significant Portuguese composer of his era, and this work serves as an bridge between late Classical structure and early Romantic virtuosity. It features a demanding set of variations that test the performer's technical versatility.
The variations require high-level technical control, particularly in maintaining clarity during the rapid ornamentation and running scales.
Comparable difficulty and character — good candidates for what to learn next.
An introduction, 5 variations and fantasie (Op.6) is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 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 An introduction, 5 variations and fantasie (Op.6) lasts about 10 minutes.
An introduction, 5 variations and fantasie (Op.6) 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 Capriccio and Variations on 'God Save the King' by João Domingos Bomtempo, 100 Variations over a Descending Scale by Vaclav Pichl, 100 Variations over a Descending Scale by Vaclav Pichl — see the full similar-pieces list on this page.