I like this song because it's musical. I say that there are good and bad musicians everywhere, and that's entirely true, but there have been quite a few songs that have proved to me that Japanese musicians are generally more musical. They have more experience, the industry has been around for longer, it's harder to survive as a musician in Japan, and generally everything about the industry pushes them to become more musical. But that's just an opinion.
The song has dynamics, it has direction, but it also has enough repetition to appeal to the mainstream audience. Add in a pinch of sophistication in every single part of the song, and you're made. The gorgeous melody placed on top of the spot-on, brilliant, instrumentation is a joy to listen to - it's so effortless, yet it's so fun. Hey, it's made me want to get up and dance at one point. I don't dance.
And, for one of the few instances, BoA's voice is bearable! (for me) I mean it's far from bad, but there are times when I just get annoyed. I wasn't this time around. That much. The gorgeous song most probably made up for it.