Piano Sonata #2 in A Major Opus 2 #2. It's part of the Op. 2 sonatas composed in 1795 and dedicated to Joseph Haydn.
The overall view of Sonata No. 2 is that it is agile, graceful, and lyrical. This contradicts its radical and revolutionary tendencies, also its enormous technical difficulty. Beethoven was determined to surpass his predecessors from the start, and this sonata is already well beyond Mozart and Haydn.
A striking aspect of this sonata is its style with the tone: it changes unexpectedly and often with an extremely modern sound; see what happens in the second thematic group of the first movement, where it moves in intervals of a minor third, the use of C and F major in the development of the movement, B flat in the second, G# minor in the third and F with B flat major in the last section of the 4th movement. It's amazing that something so elegant moves with such modulating aggressiveness, and the color that Beethoven generates with these kinds of changes explains why the romantics couldn't get enough modulations in the sevenths, sixths or thirds.
There are the textures that Beethoven uses throughout the sonata that were previously unknown in piano literature. In the 1st movement, parodic extensions of melodic forms of rise and fall so common in the classical period, with intense red-hot scales, as well as some sublime 3-part textures. In the second movement, beautiful Brahmsian textures and pizzicato in the lower registers against sustained midtones. In the fourth movement an operatic jump down, absurd, but that's what makes it great, along with a deliberately over-involved imitation of a motif taken from the first movement: an ascending arpeggio.
It is important to note that the defining characteristics of Beethoven's style already abound: lots of motivating and intelligent manipulation in the first movement and by classical standards, an unusually long movement. This opens the door to the big movements that happen in music from then on.