The good parts.
I like the male ML, I thought the charector was appealing, and the actor is like a warm hug in the role.
The thriller element was well handled at the start and the idea that the various characters are linked by the building.
The female ML, there seemed no character development, but the idea of two people gently finding each other was nice.
Bad points.
They tried to join two genres and didn't make it work, and the plot was a mess at the end.
Some story lines were totally rubbish, and my pet hate, adults in their late thirties being portrayed as immature teenagers, especially when they are supposed to have responsible professional jobs . Who would let themselves be bullied in to a spoilt virtual stranger staying in their home with no proper explanation or need?
The constant use of the plot device of people not telling people important information, and then not explaining why afterwards X had happened.
If you have worked in health care or hotels you have seen a lot of human nature, so you are not easily shocked, but you would have a have responsibilities to other staff for their safety.
The ML's relationship later wasn't treated like an adult couple, I know it may have something to do with the rating, transmission time slot, but they were still depicted as being immature in their relationship and its just not believable.
Some in another review the reviewer dropped it at Ep9 and that is probably where it should have wrapped up, as I watched it all and was really disappointed by the end.