Many interesting things happen in this piece. In the broadest sense, it is ternary. The A section, at the beginning of the piece, is 24 measures long. When it returns, it is only 16 measures long. The two outer sections seem periodic, whereas the B section, which lasts from mm. 25 to 53, sounds more like a phrase group.
The first section is a double period, each half having three phrases (I'm sure there's a term for this, but I could only guess that it's a double compound period). The first three phrases are four measures long and end with a half cadence, while the second three, though very similar to the first three, end with a perfect authentic cadence.
The middle section has three noticeable phrases that do not sound related in an antecedent-consequent sense. This melody is very interesting because many of its gestures are connected through ellision - the third beat of one gesture, which is its resolution, is also the pickup to the next gesture. After these three phrases (four, four, and six measures long) the left hand begins a swelling bass passage that lasts until the return of the A section.
The second A section is shorter because it is not a double period. Instead, Chopin just repeated the third phrase several times to wind down the piece.
Vladimir Ashkenazy's performance of this piece made me feel very intrigued, but in a way annoyed. Only during the B section was any kind of constant tempo established. This piece is very romantic - the harmony is rich and surprising and, like I said, the tempo is very straightforward. It's very interesting but difficult to analyze.