This is the third Kdrama I watched. The soundtrack is surreal, the bromance between Grim and Goblin and is just out of this world (not just figuratively). But I think that Sunny and Wang Yeo's story had overshadowed the main plotline.
Throughout the drama, the main story seemed to be hugely underdeveloped. The age gap really doesn't matter, their little moments were too awe-worthy, and the plotline was top-notch and unique. But they could've done so much better. Personally, the twist and turns were somehow bearable. I only cried on seeing Wang Yeo aka grim cry. And after a time, it gets boring. Repeating the same love speech five times isn't romantic (at least not for me).
Overall, I give it three stars. One for the wonderful music, second for the super cool bromance, and third for Sunny and Grim (and Deok Hwa!!!). The more I watched it, the more I wanted that the main plot should have been their story.