Brahms wrote it when he was 20. The melodies are warm and expressive (Brahms…). But the music is long and structurally loose. In his fifties (1889) Brahms revised it. The later version has leaner piano, the motives are more rigorous and the overall architecture of the piece is clearer — just a lot more better in all perspectives. The 2nd version is the one often performed today.
The piece is not technically demanding but actually (and well, naturally for Brahms) takes a lot of maturity to play well. You need control, patience, emotional restraint to present the textures, tempos and development in the music.
Listen, for the amount of earnestness in and sincerity at the beginning minute: