Umm...Err...I don't know yet.
The traits are quite interesting. Well, most of them are. Insane for instance opens up some really weird cool conversation paths, but absent minded just makes forget your camands, which is a pain in the arse and nothing else.
The open world aspect...isn't completely open world. You can't actually enter any shops, work ect yourself, you just see your sims go in and come out a couple of hours later which is a bit of a disappointment. Plus the you can enter a house if they invite you in, other wise you only seem though the window.
The needs and wants things has...kind of been replaced (or at least rethought) with buffs and debuffs instead. I'm not sure if this is a good thing or not yet. Basically if you have a good nights sleep, you get a 6 hour buff, if you have a good meal, a buff, a good clean, a buff, music is on, a buff. You get debuffs with your needs go down too low, like if their too sleepy or they had a bad day at work. They...they don't change that much. The way they've done the wants now is MUCH better. Now a want with come up in the top screen, and you can leave it, or save it for later. That means you don't end up with your want bar filled with impossible wants.
There a irrataiting thing though. Speed up isn't fast enough. That is really, really annoying. Theres great big huge periods in the sims where your sims are doing nothing, going to work, speeling ect and it takes FOREVER! In the sims 1 and 2 it was over like that and you could get back to the game. They really, really need to fix this. Ever time my guy goes to sleep I nearly do.
I havn't got into it yet. Maybe I'm just bored of the sims in general, or maybe the it's not enough of a change from the sims 2. I don't know...It's ok.