I adore their Japanese discog.

Honestly, there isn't a single song I don't like on either album, except for maybe Born To Be A Lady, which is still pretty.
I agree about Seohyun in TTS but not because I don't like her; I just think her voice sounds so similar to Taeyeon's that there isn't really any value in sticking her in there. I'm glad she got to show off her vocals but I'd much rather have Sunny or maybe Jessica.
EDIT: Wait I forgot about Let It Rain, I hate that song.
