I'm glad and relieved that DSP decided to steer these girls away from the mid-Kara era sound ("Pretty Girl", "Wanna", etc.) and towards something more suited to their vocals and basically something that's isn't cutesy. I think this is partially because Rainbow were around when the bigger-named girl groups were a little into the shift from cutesy to dark/more mature sounds.
None of them have drop-dead gorgeous voices (at least from what they've shown us so far), some of them still don't know how to sing live, and there are easily dozens others better at performing and singing, but their songs suit them, and like f(x), this has become their sound, this is them. There are many other groups who've come and gone and who sound(ed) like them, but the simple fact that they're able to sustain this sound for more than one or two singles means they're in this for the long haul, and they, or DSP, are really thinking about the future of the group - they are no longer an afterthought, if they ever were one.
Seeing the trend in these groups - how a lot of them slowly going their own ways musically - could very well be a signal that kpop is starting to think of putting a premium on musical identity in idol groups. I know a lot of other groups are very clear in their musical styles, but you know something's happening if a group of Rainbow's stature (which isn't really that high yet) is following too. Or I could just be jumping to conclusions. But then again, who knows what the future will bring?
So the song. The song's different from their previous single "To Me", and yet there are similar elements and sonically they'd generally be placed under the same category. It's a Daishi Dance-produced song, and it does sound very much like the Japanese interpretation of "dance" and "club" music. I was listening to the instrumental just now and I can imagine this playing in some club. Vividly.
It's repetitive, it's got all the elements of a club "anthem" so to say, but it's also very clean. Sometimes too clean. But that's the charm of a Japanese song. Once again, there are elements that really sound like a cheesecake. (if you're a newer reader, I once related Japanese production to a cheesecake and Korean production to a chocolate chip cookie with nuts)
As a whole it's one of those songs that go nowhere on the surface, but the more you listen to it the more it sticks and then you realize that even the repetition has depth. There are times when the melody is gorgeous (that part with the "sunshine" or something), and the chorus nicely balances everything out - it's a bit scream-y, a bit melodic, but very fitting to their vocals. It takes what they can do, and makes it somewhat not painful to the ears. It's not something I'd listen to with a splitting headache, but you get the point.