Oddysee, of course. God knows how many times in my childhood I had nightmares based on Rupture Farms, sligs, meatgrinders, GODDAMN BATS and Abe being shotted/eated/bited/falled to death/stabbed by Scrabans/discovered in shadows and being shotted etc. Even nowadays playing Oddysee can't shrug off feeling of Abe's weakness and how overall dangerous situations he is in.
A whole lot to this feeling of course adds sound effects like sound of being shotted, getting into meatgrinder or falling to death with Abe's loud "Aaaa...". And that creepy few music notes, which plays after you died...
Last but not least is, surprisingly, older graphics - seeing Abe and mudokons in game, without that much details of their, I'd say, cute faces manages to subconciously pretend that mudokons are humans, and playing as Abe, who you somehow interpret to be a human also causes to merge yourself with protagonist and yet again realize that GOD HOW MUCH that bullets will hurt, ripping YOUR armorless almost-naked body...
Thanks for the broken childhood, OWI!
(just joking).
N'n'T somehow was more cartoonish, I'd say "friendly" to you, with more bright colors, more detailed models (thus distancing mudokons from humans), less creepy sounds and lighter death animations. Perhaps, because of all of this (and thus less scary), it was less memorable.