Silly. The twist but mainly Dae Su's reaction to it *spoilers*
"......you slept with your daughter"
"What..? No! I will be your slave and your doggy" *licks feet and cuts out tongue*
Really? This was so silly. And Woo-jin killing himself? Why? We didn't see him in that much pain, so what was the point.
Perhaps Korean culture assigns far more shame to being a victim of incest than other places. Sure incest is pretty questionable, but when you're victim to an elaborate plan designed to set you up, I don't see why that's so shameful.