A really fun series to watch with it's own weaknesses.

The Bad(s) :
Character storylines go missing for characters who developed good enough.
Not a good ending for everyone, especially the BL/LGBTQ part and will keep making you ask "why?" (Korean series are well known for this but still could have been worse though)
Some storylines can feel like being clichéd.
The rap is really misplaced and ruins the really good bg music.
The negative roles didn't always get the same level of punishment that the good ones feared they will earn if they went rouge (this comes under the clichéd section I guess).
Once you finish, you may not want to re-watch it.
And yes, you will feel like a few cliff hangers too if you watch all characters as closely.

The Good(s) :
Amazing direction by the director.
Even though the episodes are so long, you will enjoy every second of it and never feel it is over-stretched.
The mix of emotions are phenomenal, you will be laughing out so hard and be touched really deep too, not to mention hit really hard by the sadness at times. The transitions will make you go crazy.
A never ending movie watching experience that you won't regret and you will never know when you passed almost 2 hours for every episode.
Great cast.

Conclusion :
Overall it was fun to watch with it's own frustrations and cliff hangers which probably will never be cleared and hence you won't feel like watching it again.