I have listened to a lot of Beethoven, so I am pretty well versed in his style from his middle period(which is when he really blossomed as a composer). The Pathetique sonata, although composed during his early period, is a very good example of what I mean whenever I say Beethoven's style.
These are the characteristics I associate with Beethoven's music:
- Sudden dynamic changes(both forte to piano and vice versa)
- Sudden tempo changes
- Octave heavy
- Using the minor mode a lot, even in major keys
- Overall, very dramatic sounding, even in an otherwise peaceful key such as C major.
All of these are found in the Pathetique Sonata. Also, Beethoven had a thing for C minor. His most dramatic works are often in C minor. Beethoven's music tends to be complex and it sounds as though the bass is a melody of its own, albeit very repetitive and mostly in octaves. You can't get the essence of Beethoven without the bass line. He also is one of the best composers as far as development is concerned. You don't need to look any further than his Fifth Symphony to see how he can transform a simple, short motif, to a complex work of art.
Very few of these characteristics I associate with Chopin except the sudden tempo changes. Chopin to me is more melodic in nature when it comes to his music. His bass line tends to be an ostinato and most of the beauty comes from the melody alone. If you just played the melody without the bass line, you would still get the essence of Chopin. Also, another thing I associate with Chopin is having the rhythm in 3s. He uses triplets a lot and I really mean a lot.
His Nocturne op. 9 no. 2 has triplets in 2 forms. First there are the explicit triplets where you actually see a 3 above the notes. But most of the triplets there are implicit triplets in the left hand. He basically wrote it in 4/4 but decided on a 12/8 time signature to avoid lots of triplet marks. But I mean really, 12/8 is the triplet form of 4/4 so me saying that there are implicit triplets in his most famous nocturne is very accurate.