What annoys me is that the MC doesn’t even try to understand the antagonist’s motives. He’s like a mindless puppet handed a sword and told, "YOU’RE the hero, and THAT guy is the embodiment of evil—you MUST kill him!" And so, the hero mindlessly charges in, swinging his sword without asking a single question. What’s worse, the Dark King has reached out to him mentally multiple times. I was hoping for at least some NORMAL conversation with the antagonist, but the protagonist just acts like a brainless child, constantly screaming, "I’m the hero here, and I’ll kill you!" without ever asking a single reasonable question.
It would be interesting to see an alternate version of the story where MC secretly aids the antagonist. If the whole corruption theme is just a lazy setup for a generic "good vs. bad" ending, that would be disappointing—at least for me as a reader.