The reason why I'm slightly in love with this? The song's probably K-pop's closest and best-done shot at a Swedish pop song - there are parts that I can imagine Darin or Danny singing. And that's a compliment.
It's got a very simple yet gorgeous melody, a catchy chorus, and those Ola/Danny-like synths throughout, not to mention a really upbeat guitar line. If that's now Swedish, I don't know what is. So it is.
And to be honest with you, the recording came out quite good. They don't have the best live vocals around, but they sound perfectly fine here, and the song works to their advantage - the melody matches majority of their voices nicely. I mean it's not magical or anything, but listening to it isn't a pain or anything. At least it doesn't sound like a trainwreck, because a lot of songs this year have been disasters.
I'm not so sure if Infinite will be able to sustain what they have with this song, much less better it, but let it be said that She's Back is a fine piece of pop music.