Nate, I've been saying this for years as part of the #EAListen movement on Twitter.
1) We need the diametric personality sliders (Sims 2 style) e.g. active-lazy, outgoing-shy, neat-messy. This is the CORE Personality. Sims AI (what actions they choose by default), as well as the animation styles that are used (such as how they react or talk with other sims), are DETERMINED first by the core personality. I detest that EA threw this amazing personality system away in favor of Sims 3 traits
2) HOWEVER, traits still have their place. Traits ON TOP of personality adds additional flavor.
A good question: why can't traits alone suffice? Answer: the act of forcing the core personality into a diametric slider of extremes (e.g., strong active, neutral, or strong lazy) as well as over a fixed number of dimensions (5 aspects of personality in the sims 2) that is consistent for ALL SIMS no matter the future expansion packs make the personality ACTUALLY PROGRAMMABLE AND LOGICAL.
It's reasonable to make animations and AI decisions by saying....okay, if your Sim has at least 7 out of 10 in the direction of active, we're going to give them the quick get-out-of-bed animation instead of the slow get-out-of-bed. Basically, every Sim can get be bucketed into one of the extremes or neutral for every personality aspect.
With traits...there is an effectively infinite number of them, and they range in type. A "vegan" trait is different from a "neurotic" trait which is different from an "ambitious" trait. Sure, you can program specific quirks or abilities for each trait, but they range in type and not every Sim has a degree of strength in every single trait. This makes programming animations and AI difficult for every single trait. The problem expands when you add additional traits.
