Marco Anzoletti's variations on Paganini treat the virtuoso theme with a dense, post-Romantic harmonic language. It demands high technical facility and an ability to navigate complex keyboard writing.
The primary challenge lies in the rapid execution of wide-span broken chord figures.
Comparable difficulty and character — good candidates for what to learn next.
25 Variations on a Theme of Paganini 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 25 Variations on a Theme of Paganini lasts about 18 minutes.
25 Variations on a Theme of Paganini 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 Allegro di Concerto in E minor by Marco Anzoletti, Ballata No.1 in G minor by Marco Anzoletti, Ballata No.2 in B-flat minor by Marco Anzoletti — see the full similar-pieces list on this page.