So ngl, I'm generally not one for the mystery genre, as, well, to my limited experience, they're all pretty poorly executed. I understand WHY they're popular as a genre, and how they can involve the reader, but probably because I tend to stick with shounen versions, they're poorly done. And while I can't say this one was perfect with no plot holes, it was pretty well done.
TBH, i came here for the romance first, and it was pretty cute and well done. It also served a pretty integral part of the setting, i.e. why the MC and cast are so invested in what starts out as a totally unrelated girl's apparent suicide.
So yeah, there are a few plot holes, but that mostly stems from the ...hmmm... supernatural aspect? Essentially, there's a time-traveled ghost, while the female lead is actually still alive They also hop timelines to an alternate world, and then back again, which makes the plot a bit murky. Also, the ghost doesn't really remember how she was killed, but occasionally she'll recover some memories that will help the plot, so it's kinda Deus ex Machina at times. To be fair, they're pretty minor, but it's not like the plot is a procedural that purely involves logic.
I guess to sum it up, I would say that it's not at all for hardcore fans of mystery, but caters to someone who might be a light fan of the topic. Which in this case, I quite fall under.
Most importantly though, the ending is good, and everyone save the initially dead girl and the antagonist(s) end up happy. Which is rare when ghosts are involved. But yeah, I enjoyed my read, and would recommend it. Just don't go in with super high expectations on a perfectly written crime/mystery story.