All the music was top notch, particularly the World 2 theme as you are in the Iceometric Palace.
However in this day and age of modern gaming, video game music has sadly been sorta pushed to the background. As video games have become more about story, presentation, and immersion, music is used less often and when it is used it is used in a far more atmospheric and subtle way. It's sorta there to support what's going on without being 'distracting' It's now very akin to how a movie uses music.
I think YL leaned just slightly too much towards this atmospheric/subtle style.
I wanted the more old school catchy melodic style tunes. In the 8, 16, and 64 bit eras of gaming video game music was just much more noticeable. It seemed to be more in the forefront, with catchier tunes and stronger melodies. Video games were games, not movies, and as such they had catchy music in almost every level (or at least that was the idea).
I hope in YL2 that the music is more this old school style. All the world themes are fantastic but are generally too slow in rhythm to be catchy. All my favorite parts of them are when they are faster paced and more noticeable. In other words the music doesn't need to be subtle, let it shine in the forefront.