This monumental set consists of twenty-five variations followed by a massive fugue based on a theme by Handel. It stands as one of the greatest examples of the variation form in the piano repertoire, demanding immense intellectual and technical depth.
The player must maintain absolute control of polyphonic textures throughout the variations, culminating in the taxing and complex final fugue.
Comparable difficulty and character — good candidates for what to learn next.
Variations and Fugue on a Theme by Handel (Op. 24) is rated Henle level 8 of 9 — concert repertoire, roughly diploma level. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 8 — meaning you can already play level 7–8 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 Variations and Fugue on a Theme by Handel (Op. 24) lasts about 28 minutes.
Variations and Fugue on a Theme by Handel (Op. 24) 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 Rhapsody in G minor, No. 2 by Johannes Brahms, Hungarian Rhapsody No. 2 in C-sharp minor by Franz Liszt, Bourrée fantasque by Emmanuel Chabrier — see the full similar-pieces list on this page.