This is one of Chopin's largest compositions for solo piano, typically lasting well over ten minutes in performance. It is unusual not only in its length but in form: some have called it the "fifth" Ballade, but its 4/4 time, as opposed to the usual 6/8 of the ballade, perhaps ruled out that genre name. Certainly the work qualifies as a Fantasy in that it is loosely structured and extended, profuse in its melodicism, and quasi-improvisatory in nature. The ideal of unfettered imagination was a strong one in much of Chopin's music, however, and in fact this Fantasy bears some affinity with other big Chopin pieces of the early 1840s, such as the Scherzo, Op. 54 and the second and third piano sonatas. The work shows this master of the miniature applying himself to the problem of large-scale form, and in this respect is very much a worthy counterpart of earlier composed Fantasies such as Mozart's K. 457. The challenge composers faced was to avoid the seeming contradiction between the ideals of composition and fantasy.

The piece starts off with a slow march-like theme which appears only once in the piece. There follow three main groups of themes, each preceded by a sort of bridge passage that serves as a refrain. This bridge is made up of arpeggios that rise upward and gradually increase in tempo. The mood imparted by the first group of themes is one of intensity and passion, of drive and excitement. Its chief theme is stormy and somewhat melancholy, and is the most dominant melody in the work. The mood of the second theme group is subdued and has an air of religiosity about its solemnity, while that of the third is a mixture of triumph and happy defiance. The refrain closes the piece, leaving the listener in awe at the many moods and colorful writing he or she has encountered in this somewhat enigmatic work.