I absolutely love this soundtrack, but I think the Concert Hall songs sound really off. It seems like the Concert Hall songs are missing some instruments, making them sound rather empty or "incomplete", such as the Ballad Song not having any beat for some reason.
The songs I'm referring to are Ballad Song, Enka Song, Metal Song, Musical Song, Opera Song, Pop Song, Rap Song, Rock & Roll Song, and Techno Song. The Enka Song sounds the most like what it's supposed to be, but it still irks me that there's some difference/off-ness.