I happened to attend a local concert of the First Piano Quartets by Mozart and Brahms, both in the key of g minor. It was an interesting idea for the organisers to juxtapose and, eventually, compare these too significant and pivotal works in this rare medium of the genre of Chamber Music with Piano.
For Mozart, any work in the minor mode plays an important or at least interesting role in his vast Opus. He was so inextricably linked with the tragic power of this key that people usually overlook that he only wrote five works in g minor, three of them in his Chamber Music (his magnificent String Quintet, K.516 and one of his two Variation sets for Violin and Pianoforte, the K.360, and the First Piano Quartet).
The work is an example of a perfected and at the same time superbly inspired and developed specimen of this medium, with a unique and impressive First movement heralding even Beethoven, a gloriously gentle slow movement in the relative major (B-flat) and a greatly formulated and inspired Finale, in a rather complex Sonata-Rondo form, in the tonic major (G major).
On the other hand, the First Piano Quartet by Brahms is a very important work both in furthering of the medium, particularly in the Romantic period but also in the development of the composer. It is a work of huge proportions, expanding on other already large works by Brahms. Each movement is laid out on an almost gigantic scale, using at the same time a turbulent Romantic musical language with a self-assured and almost symphonic mastery of musical design.
This monumental and exhausting work has four well-conceived and developed movements: a gloriously complex First Movement of a sprawling exposition and a well-elaborated development in an expanding Sonata-Form, an extended Second Movement called "Intermezzo" (intead of a brief Scherzo) in c minor, a most beautiful and intensely lyrical slow movment (the only movement in a major mood, in E-flat) with an assertive central march in C major and a virtuoso showpiece as the Finale, almost a tour-de-force of exhilarating rhythm and melodic invention in a well-sectionalised Rondo of clearly gypsy-inspired music.
Based on the interested forum-members (if any), we might examine each movement separately along with various notable recordings.
If interest goes, by any chance, further, we might also throw some light in Faure's Second Piano Quartet, also in g minor, although not a work in the same league as those by Mozart and Brahms.