I finally bought the game tonight at Target, installed it, and played it for over a couple of hours just to get a general feel of the gameplay.
As
Alicia pointed out, some things are the same as or similar to TS2 (e.g., Careers, aspirations referred to as "Wishes," Skills, etc.). Yet they've also added some new features like Traits (which are a combination of six different personality aspects you pick for your sim, a huge leap from just choosing a Zodiac sign).

I also like the new Create-a-Sim menu, which is a lot more dynamic than TS2.
As for the graphics, I have to admit, I'm a bit disappointed here ... The character renderings are different from those of TS2. Don't be fooled! When you look at the DVD-ROM case and see those different sims on the label , the actual characters are not as good as they are during gameplay. I tried playing a pre-created sim family as a sample; I wasn't too impressed with the appearance. It almost reminded me of the time I briefly experimented with
Second Life on-line--the avatar/character drawings didn't quite meet my expectations. I don't know ... Maybe the characters I played had darker skin tones and looked rather boring. For that matter, I think TS2 characters (which I still play) appear much better.
I haven't had a chance to build a house yet, so I can't comment on the Build Mode.
The gameplay is essentially the same as TS1 and TS2; the only huge differences are the scope of the environment and the saving process. When I play TS2, the main focus is on the individual sim(s) in a particular household or lot. I choose the family/household I want to play (consisting of one to eight members), wait for the lot and corresponding sims to load, play it, and then save or abandon changes when I exit. Saving is "native" to the household I've just played. In TS3, the process is the same in that you get to focus on one particular sim or household, BUT when you quit or exit the game, saving is done "globally" so that the changes are applied to the whole community you're playing (e.g., Sunset Valley), rather than just the current household. For every time you finish playing a family lot, you are prompted to save
and name/rename the community/family you've just played.
Does this make sense? It's almost as if you're playing a PS3 game and the system asks you if you want to save your "progress" up to that point, and you get the option of either replacing the current game data or creating new data. I'm not necessarily saying this is a bad thing, but in the process of saving and creating different save files, it's almost like creating different
alternate realities for the game.
I gave this game a "Good" rating because I don't feel it's on the same level of quality as TS2. Who knows? When they start releasing expansion packs for TS3, I just might get accustomed to this game.