This Game really surprised me in both positive and negative ways. Mixed feelings about the unopened world, takes a bit of the fun, but with the m-a-j-o-r lagging problems of The Sims 3, I guess that's like putting pants on when you have people at home: like it or not, you got to do it.
On the bright side, socialization is WAY more interesting, as already pointed out; the metrics of jobs, skills, dates and the game as a hole gives you a sense of micro achieving which wasn't there at The Sims 3, where you had to play for (human/real life) hours until you actually accomplished something; the game is harder now, getting superrich, superfriendly or superskilled is not a "natural consequence" of playing as in The Sims 3, you must really work and plan for it; last but not least, wish management is much better, as it avoids the I'm-about-to-clean-the-dishes-but-can't-promise-it-without-erasing-one-of-the-4-highly-rewarding-promises-I've-already-made frustration.
The down side for me was mostly the graphics. The camera angles are a mess and the cartoonish look of the sims and objects (not a bad thing) is followed by - suprprise - a lack of over the top animations which are so fun in The Sims 3. Whohoo is the greatest example: in TS3 it's "come here, you're mine!", while in TS4 it's more like "I'm bored, let's whohoo/Yeah, why not?"
On a final note: change the pause button to [zero], really? You know 90% of mankind is rightly and, therefore, plays with the left hand on the keyboard, right? And the other 10% cannot enjoy this brilliant innovation if their playing on laptops without numerical keypads.