Oh! Oh! Talking about characters are we?
Based on several games with interesting characters that I’ve played, I think what make them truly shine is that they are more than what meets the eye. While likeability is a very personal thing, most if not all of those characters have their own set of quirks, hobbies, backstories, and things that just make them interesting if not downright endearing.
It’s one of those things where you go “Ah, it must be this person.” when you read a dialogue and actually recognize the character speaking it. I guess that distinctiveness is just what make the characters stand out more.