Cave Story fans when Undertale gets more popular because it doesn't rely on dumb fetch quests like finding dogs when it wants to be lighthearted; and because it doesn't have possessed or cursed enemies with no agency over their actions (like fighting you because eating some flowers make them violent or because a controlling device forces them to) so the story becomes dark in a sensationalistic way with a cartoonish evilllll villain, but instead willingly attack you because of empathetic and organic tragic world building reasons and the main antagonists have motives foreshadowed through the game instead of all the complexity being reduced to a character dumped at the last second:

>>>:O

But seriously speaking, I felt there should have been something more palpable when exploring the underground, given that the robot you control is considered throughout the game to have been once used to exterminate the creatures you encounter (although it's later revealed that your specific robots protagonists didn't have anything to do with the incident, removing the guilt that made then more interesting characters and which propelled them to help these things in the first place).

I feel there's only an instance of this feeling of hostilty you would expect in the final area, where the mimigas seem to be working for the doctor for their own protection out of fear instead of being forced by script manipulation tactics of singular characters to kill you, but this instance and that corridor with the deformed baby dragons you were expecting to hatch since the beggining of the game, which with no words leaves a very saddening impact equal to Crocomire's encounter in Super Metroid, are few and far between and the game doesn't have that attractive of an atmosphere to make up for how basic it felt.