These are English lit classes ramblings influenced by me, haha, so bear with me...

It isn't always the uniqueness or complexity of the character makes it interesting. I think that unique or complex characters should be avoided, at least in a roleplaying forum. Most films and literature cannot handle such characters properly. It's more about what you do with a character concept, in the character's arc, than anything else. My favorite villain of all time is Kruger, portrayed by Sharlto Copley, in the film "Elysium"; the character concept is so simple, yet it has such depth due to his performance and what they do with the character in the film.

Most characters tend to fall flat when it comes to their flaws. Authors and writers are too blunt about their character's flaws, especially when they are unique or complex, almost to the point of simply stating "this is the character flaw." However, if you properly present a flaw in a character's arc, over time, even the most mundane, boring character concept will have depth and be interesting. Always assume that people are stupid, so the core concept must be simple. The uniqueness and complexity should lie within the nuances of that simplicity, its presentation.

I don't think it would be fair for me to discuss Olivia, because I'm the GM and I can approach things in an entirely different way than you can. However, her flaw is not particularly interesting or unique (obsession), but it's in its simplicity that I can really create something and add depth over time, and use it in her character arc in a meaningful way that is coherent: the flaw is coherent to her character concept in the sense that she is caring for something, but to an unhealthy degree; there is a trigger that bluntly states when her obsession is shown (Samuel); and it is slowly changing her parallel to the story (character arc).

On a roleplaying forum, I think it's important to have simple character concepts and then play off of the nuances. People will instantly understand it, as they can easily comprehend the character concept. Never underestimate the stupidity of stupid people. Not that I think that you guys are stupid, you guys are smart and I love you!