Not a bad read, but, at least in my eyes, with a somewhat disappointing end.
Bastards main strength lies in the protagonists father. The Serial killer. You can very much relate to jin, his son, and the terror he feels towards his father. Not because of the gruesome murders, but because of the mental abuse. Dongsoo (the father) is an intelligent, cruel, manipulative monster that drives his victims insane. He keeps his son as a pet to assist him in his murders and uses his role as a father to lure in new victims and appear innocent to the public. He enjoys the security his approach has given him, as well as the power he holds over his son. When Jin (his son) now starts to rebel against him his father begins a cruel game.
This is what gave the manga strength. This was done very, very well. Sadly in the end it seems the author could not find a way to lead this to a fitting conclusion. Instead he (or she?) decided to go with a character twisting final reveal that seemed to be more shocker than actual substance. This broke the dynamic that worked so well for this story.
In the end this is an entertaining read that works based on the described relationship and the thrill it creates, sadly this is done at times with somewhat silly story developments. This would have been forgivable if the ending had landed, but sadly this was not the case.
So final verdict: a fun read, with hints of greatness, and sadly nothing more.