Now, we have to separate two different kinds of thrills - the absolute terror and the rapture.
The winner in the first category is Homelander. I don't think I genuinely feared the character as much as him. We spent HOURS discussing him with a friend (hi, Wąż Jadwiga) after each episode and while the series progressed, we were just in more an more awe (in its most simple meaning as "a feeling of reverential respect mixed with fear or wonder"an emotion variously combining dread, veneration, and wonder that is inspired by authority or by the sacred or sublime", Merriam). Whenever he dons a smile on his face, a person feels there's a hell to unleash behind it. Not having any human connection since birth and being raised by steel floors of laboratories, Homelander grew to be completely barren emotionally and unflinching. He does not hesitate to kill the plane full of people just to help his own agenda. And worse - to deliver a moving eulogy afterwards.
There was never such consistently and pervertly immoral and threatening character on tv screen. Nay, not even in the movies.
On the other side of the spectrum is Nokdu. I'm writing, day by day, a review, so I will indulge my scribbler nature and write more, but for now I have to admit - among other genuinely good guys 2019 gave us, Nokdu probably gave me the most feelings (part of it was figuring out where the acting ends and how much of Nokdu is actually JDY, but I digress). A guy who was split into two halves - one was the caring, tender young man, always speaking his mind because not having anything to loose, and the other - a ruthless killer when the need called for it. He glided between those in the latter episodes, but never crossed the line, even though he was really, really close. That dichotomy was fascinating to watch.
Honorable mention:
Yu Jiho - his whole heart in the palm of his hand. And overwhelmed reaction when he heard he was loved. A quiet, patient man giving the woman he loved all the space she needed. The world needs more of such souls.