I think the concept here is quite good; the problem is the uneven execution. I love the idea of an exceedingly ordinary (random) guy getting superpowers. The way he starts realizing something has changed (and then starts experimenting) is very cool. However, the idea that this guy abandoned his family seems contrived, and if we are to accept this, there should be more depth than just animosity from his estranged daughter. It also bothers me that the guy walked out; I thought personal responsibility was a big deal in most eastern cultures.
I've seen a few other oddball South Korean S/F films, and there is a standard theme that family is important, but "family" isn't just people you share genes with (or married). Those themes are present here, but they feel a bit superficial and unconvincing -- it's like some realism is missing (such as press coverage, proper scientific investigation of blatant physics-defying abilities, and military interest). The return-to-quasi-normalcy ending seems loosely modeled on The Wizard of Oz, which works great in a old-time rural fantasy, but less well in a modern urban setting.
Jung Yu-mi is fantastic as a psychotic mob-boss and corporate executive, though her screen-time is very limited.
The special effects are good, but the audio volume varies considerably from one scene to another. The music and sound effects are often much louder than the dialogue.
I give this 5.5 stars for the (fresh-but-flawed) entertainment value, with a half-star bonus for Jung Yu-mi. That's six (6) stars total.