Louis Brassin's virtuoso transcription of Bach's monumental organ work brings the power of the organ to the piano keyboard. It is a staple of the Romantic bravura repertoire, demanding immense technical control.
The technical hurdle is maintaining clarity and articulation in the rapid passage work while managing wide-spanning octaves.
Comparable difficulty and character — good candidates for what to learn next.
Bach- Toccata and Fugue in D Minor (Transcription) 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 Bach- Toccata and Fugue in D Minor (Transcription) lasts about 9 minutes.
Bach- Toccata and Fugue in D Minor (Transcription) 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 Ballade No.2 by Franz Liszt, Piano Sonata No. 23 'Appassionata' by Ludwig van Beethoven, Variations sérieuses by Felix Mendelssohn — see the full similar-pieces list on this page.