The Good
⌲ There are some extremely touching emotional moments.
⌲ The main characters were excellent. (ML, FL + 3 ghosts)
⌲ Jin Ki Joo is really awesome in this, what's up with all the hate???
⌲ Park Hae Jin was quite alright too, he has improved A LOT since My Lover From the Star.
⌲ The romance is pretty good, albeit way too slow.
⌲ The ghost related side stories, crime solving (not quite as good as in Goblin, but far above average)
⌲ The comedy
⌲ The second couple was quite fun, though they had very little screen time, or plot significance.

The Average
⌲ The love triangle (considering all the sageuk vibes, this was quite tolerable)
⌲ The show has many extremely silly moments. (some of them were quite out of place)
⌲ The plot
⌲ The ending (the five minute long happy ending does not completely justify the entire final episode and it's just too fantastical, even for a kdrama)
⌲ The "general"

The Bad
⌲ The directing is strange in many ways. (Mystic Pop Up Bar is from the same writer & has a similar plot, but the contrast is quite large in this regard)
⌲ The drama is too sageuk-like for contemporary fantasy. (and I'm not talking about the S. flashbacks)
⌲ The 90 minute long sageuk flashback
⌲ The Saesang fandom in the three kingdom era
⌲ The mandatory noble idiocy breakup x2 (once in the long flashback, once in the final episode that lasted for 5 minutes)
⌲ The 2d villains are less than whelming & super stereotypical