The problem with the current personality system isn't not enough detail, it is too much detail. Or too much meaningless detail, because you have things like "liberalism", "self-efficiency", "vulnerability", and dozens others. These are scales you don't even perceive or judge in everyday life, but every dwarf has a rank in each of these, which leads to a huge list of random attributes that you can't really make heads or tails off. I never could translate the DF personalities to a coherent idea of who the dwarf is. If there weren't there, it would be basically the same. At the same time, the game is not able to grasp and communicate as simple character features as "cruel", "selfish", "kind", "evil," "arrogant," "innocent", "ignorant", "shy", etc. which are labels we use in everyday life.
In other words: the game uses an artificial, mechanical, and politically correct system of expressing personalities. A system that is useless in the end, because when we talk about people or tell stories, we don't operate in a mechanical way. Toady said in one of the DF talks he would like to gut the current system and replace it with something which feels a bit more like a story, a book - when an author is writing a novel, he doesn't take his characters and assign each of them values from 0-100 on 30 different personality scales. He sticks labels like "manipulative bitch" or "helpful uncle" to them and works with these. So presumably, the personalities rewrite means a move from numbered scales to more lively and less number-based tags and descriptions.