The story is okay, OST is okay. The ending makes you question why you liked it.

Maybe SSH had this written into his contract.
 
"The ending has to be vague or, suck altogether. Oh yeah, and let's have Halloween-Christmas because, Why not?
 
I want my fans to prove they love me for me instead of my work, just like Lee Min Ho.
 
Come all my pretty lemmings and I'll show you a cliff. Bwahahaha!"

Don't watch the last 10 minutes of the final episode and you'll be better for it.