Ludwig Thuille was a contemporary of Richard Strauss, and this work reflects the thick, harmonically dense textures of late Romanticism. It is a virtuosic piece that demands a mature tone.
The main challenge is balancing the dense chordal textures to ensure the melody projects.
Comparable difficulty and character — good candidates for what to learn next.
Allegro Giusto (Op.39) 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 Allegro Giusto (Op.39) lasts about 4 minutes.
Allegro Giusto (Op.39) 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. 8 'Pathétique' by Ludwig van Beethoven, Balada mexicana by Manuel Ponce, Allegro Appassionato by Alexander Scriabin — see the full similar-pieces list on this page.