Answer&Explanation:
Beethoven always seeked to stretch and expand the bounds of classicism; you can clearly see this in his works. One of his greatests abilities was his perfection of form in music. He continuously experimented and developed this form, which was quite unconventional at his time. For example, look at his Eroica symphony. It was twice as long as the common symphony during his day and age. The development section of the first movement broke the norm that ‘the development section should only work with the previous themes’ by introducing new material.
While the final movement was often a swift and light movement, Beethoven basically ditched this by making the last movement often the weightiest. We can see this in many of works such as Op. 27 no. 2, Op. 57, Op. 92 etc. In Op. 12, the first movement is not in sonata allegro form. Instead, it a set of variations on a theme. In the Moonlight sonata (Op. 27 no. 2), he keeps the slow movement ahead of the fast.
Beethoven also expanded the sonata form, which he had perfected very well. If you listen to the last movement of the Appassionata sonata (Op. 27), you will notice that there is a general lack of repetition of the exposition; only the second part is repeated. Beethoven also introduced newer themes in his coda, sometimes lengthening it enough to make it feel like ‘a new development section’.
Beethoven also made his music more personal and intimate. Wilhelm Kempf called the third movement of the Hammerklavier sonata (Op. 106) as "the most magnificent monologue Beethoven ever wrote". Furthermore, Op. 106 was a mammoth in its own right; it was longer than any piano work people had seen till then.
Beethoven experimented with dynamics a lot, often preferring sudden changes in dynamics. He expanded harmonic and melodic lines and frequently preferred to use lower registers and dissonance. This gives his music a darker feeling than the light-esque music of his day.
