It is described as having "ecstatic technical virtuosity and [also] mastery of form" by one commentator (Uwe Kraemer), and "elemental and unbounded power ... that only with difficulty abates sufficiently to give place to the logic and balance of the Fugue" by another (Hans-Joachim Schulze).
There is, however, reason to believe that it was not originally written for the organ. Peter Williams, in his paper "BWV 565: a toccata in D minor for organ by J. S. Bach?" in Early Music, vol. 10, July, 1981, pp. 330-337, was perhaps the first to raise this issue. An article for www.bachfaq.org by Tom Parsons explains this in detail. The following is a shorter outline of the theory.
The most notable argument is that both the toccata and the fugue are, harmonically and contrapuntally, very simple in comparison to most of Bach's organ works. The entire composition also contains many stylistical features that are obviously atypical of Bach. There is little doubt, however, that Bach did in fact originally write it--the perhaps most likely possibility is that it was originally written for unaccompanied violin. Although the whole composition is very simple for a Bach organ work, it is very advanced, and highly idiomatic, for the violin. Moreover, there is a clear case elsewhere in Bach's work in which a solo violin work was retranscribed for organ: the Prelude first movement of the Partita in E major for solo violin BWV 1006 was recycled by Bach as the solo organ part of the opening movement of the Cantata BWV 29 Wir danken dir, Gott, wir danken dir.
In Williams's view, Bach's original violin work was most likely arranged for the organ by someone else (possibly contemporary to Mozart, or even later).
These arguments, of course, are far from conclusive, and, there being no surviving autograph copy, we will never know for sure. And although the organ work might not be directly from Bach's hand, and certainly is not typical of his organ works, it is undoubtedly worthy of Bach's name.
During the 20th century, it became popular for artists to adapt the Toccata to their own esthetic agendas. Around 1927, the conductor Leopold Stokowski transcribed the work for a very large symphony orchestra, making it into a showpiece of orchestral color, virtuosity, and sheer volume. For many contemporary listeners, Stokowski's transcription serves as the principal memory of an approach to the performance of Bach that was widespread in the first half of the 20th century.
Later, the piece was repeatedly incorporated into works of popular culture, including the films Fantasia (featuring Stokowski and his transcription), Rollerball, Sunset Boulevard, 20,000 Leagues Under the Sea, and the musical/film Phantom of the Opera.The Toccata in the 20th century