I'm not frustrated or disappointed. But it's a bitter end certainly - for everyone. Still, I anticipated each episode, and maybe it's exactly about this. That nobody won in the end and paid a price for whatever they may have or haven't done. I do feel sad, but I do think as well it was one way to solve this. Each character had some "good" or "bad" sides, I even felt sorry for Seong Jun from time to time, even though he deserved what he got. Same with other characters. Maybe even Do Jun or Jin Yang Cheol who lost his hope quite early. In death, they're all the same, no matter if rich or poor... no matter what reasons they had.
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Still, I absolutely recommend this drama!
https://www.viki.com/tv/39080c-hit-the-spot