The ‘ugly’ part begins at around 4:41. Don’t get me wrong, the music is beautiful and the scene before it very powerful: your faithful companion is slowly dying, and your task is to bring her to the castle as soon as possible. However, when the player comes close to an enemy, the music switches to the standard encounter music, which makes this game sequence that much worse. Why doesn’t the piano music continue? Why are there even enemies to fight on the way? It’s not like the player will take his sweet time to kill them.
This sequence would have been so much better if the music would continue playing, even when eventual enemies are close, and the sounds Midna makes become more critical as you come closer to the castle.