There are some features that the game has that are a step up from Sims 2, naturally, like CAST for example, and a few new building features are an advantage
over Sims 2. Although, there are some limitations too in comparison. The new interactions are nice.
I've experienced a few annoyances so far, like clock speed doesn't work as it should. Also, I've noticed that they use up energy fast and it the game takes up a lot of time to get their energy level back up. I'm assuming there are bugs. There always bugs in these games. I've heard turning off story progressions doesn't work right, but I haven't played long enough to notice it myself. There has been talk of there being a limited amount of content in the game, but that might have to do with the sims store being a new feature, and they charge a lot for store items.
In comparison, in terms of gameplay, I still prefer the play style options of Sims 2, the gameplay options for Sims 3 are kind of limited. I got bored with it quicker than I thought I would.
There are a lot more reviews (good and bad), on some sims forums, where people are discussing the game in more detail than I can.
I've experienced a few annoyances so far, like clock speed doesn't work as it should. Also, I've noticed that they use up energy fast and it the game takes up a lot of time to get their energy level back up. I'm assuming there are bugs. There always bugs in these games. I've heard turning off story progressions doesn't work right, but I haven't played long enough to notice it myself. There has been talk of there being a limited amount of content in the game, but that might have to do with the sims store being a new feature, and they charge a lot for store items.
In comparison, in terms of gameplay, I still prefer the play style options of Sims 2, the gameplay options for Sims 3 are kind of limited. I got bored with it quicker than I thought I would.
There are a lot more reviews (good and bad), on some sims forums, where people are discussing the game in more detail than I can.
Remember
in Sims 1 & 2, the sims get stuck in the pool if you take away the ladders...in the new one, they can lift themselves out. 
