Simply put, this album is a masterpiece.
This album takes you on a musical theme park ride, shifting between quiet melodic ballads and harsh, dissonant choruses. The amount of detail and thought that went into each of these songs is simply not found in today's music - each note was carefully placed and each line has a purpose.
This album formed an entire genre of music, since it was so innovative even today. Incorporating jazz harmonies into more traditional rock/metal formed an interesting blend that King Crimson used extremely effectively.
There isn't a single song that isn't worth listening to. There is something unique to each track and that is something that for the most part, hasn't been replicated since.