I got to play this a bit at GameStars Live and I was very impressed. The 2nd game felt very much like an expansion pack for the 1st, well that deffinitly won't happen this time. Obviously the graphics have seen the biggest improvement and for anyone worried about how it will play on their machine the detail levels on almost everything can be changed (Think I saw about 8 - 10 detail sliders).
It plays just like the older games (deffinitly a good thing) but everything has just been taken to the next level.
I noticed guests go around in parties which I thought was a nice touch.
My only complaints would be the day-night cycle seems a bit fast (although at least putting lights in now will have an affect on the game) and I hated the gui. It felt very Windows XP like, I'm sure it will grow on me but even the person who was demonstrating the game to me had problems finding stuff.