The Sims 3, unlike a fair few reviews like to suggest, is actually very well executed, deep in gameplay, much more forgiving than 1 and 2 and most importantly brings a whole new level of fun and interesting features to the Sims franchise. Without going into crazy detail (you can probably access a much better credible source from a review site), for me, the game looks, plays, sounds and controls in the way I feel is a true evolution for the franchise and definately trumps in the new gameplay areas explored.
My only concerns are the initial lack of objects to purchase -- having the ultimate dollhouse aint so ultimate since you have less to choose from compared to 1 and 2 (No hot tub sex!!!). This is said to be rectified through micro-transactions through the online store (A scheme I am not entirely at ease with) and future expansions.
My other concern is the hardware demands on the user. I have noticed that many people are trashing this game simply because they can seemingly not run it properly. I play the sims 3 on a current gen macbook I bought last October. Despite being very much a target system to support a current-gen game, I must run my game on medium details to maintain a stable -- but never silky smooth -- framerate, and this only dips when introducing more characters. However, I simply cannot suggest that this is the games fault. There is so much happening in this game that you WILL need a good machine to run it on else you WILL have to scale back the details. Pay premium to play premium, it's simple. The animations are excellent and the AI --though sometimes curious to it's decisions and logic-- are a step up and will drain your resources.
This game does have niggles and does require a good machine to run it at a level I'd say was acceptable. However the scope of the game, the reward and funfactor are spellbinding and well worth checking out.
Patches are released to address issues such as buggy AI, crazy instances, crashes and the rest so it can only get better, and with the horizon undoubtedly rife with expansions this game will only get bigger and more consuming of your time!!
Hope this helps:)