I am actually really looking forward to this game. The Sims 3 was two steps forward but one leap back making a game that is both inferior and superior to the second.
The largest mistake being that The Sims 3 engine was very antagonistic towards expansions and even user content.
If they fix everything that was wrong with The Sims 3, add in all the functionality it required, bring back the features that the game needed, fix up the sims personality, and add a bunch of their own content.
It really could work.
Examples of the give and take of the Sims 3
Sims Personality
Good: The trait system allows your sims to have quirks and eccentricities that the sliders couldn't provide
Bad: The trait system doesn't allow the fully faceted personalities to be expressed making all the Sims somewhat bland.
Pets
Good: Pets are now full sims in their own right and it is easy to ignore them unlike The Sims 2, if you so desire.
Bad: There isn't much for Pets to do anymore and their inability to get around can really mess you over. Dogs are brokenly good at finding expensive gems.
Supernatural Sims
Good: A on-off switch, ability to make Sims in supernatural form (later on), Some super naturals are actually great and I love the ghost gimmick.
Bad: Most are too uninteresting or slow, They are FAAAAR too populous, quite a few are "better then Sims", The Robotsims are far inferior to Simbots, some don't have any traits at all, People never get used to them, There isn't enough bad aspects of them, many cannot be customized.
Expansions
Good: With the amount of expansions it has perfected the expansion type formula. A mix between previous expansions and new ones. As well as giving the best Pets expansion of all the Sims.
Bad: The expansions do not mix well and are often broken with other expansions, they are incredibly glitchy, Some expansions do not update base content (for example the Piano skill doesn't help with the music career).
Collectibles
Good: Items strewed around town that are worth cash and can be collected by us excessive collectivists? Awesome!
Bad: There is no good way to display collections nor a way to really use them for anything interesting. In fact the only Aquarium in the game only has digital fish. Bug cases, brick stacks, and heck a Gem display would have been great. Giving them a use would have been better.
You can see why I want the Sims 4... All the good is there, the bad just needs to be taken away or the good needs to be supported.
Though let me be straight. The Sims 2 is the better game, it is just that the open neighborhood of The Sims 3 is so convenient that it is hard to give up.
In a similar way that Monster Rancher 2 was better then 3... but the encyclopedia made going back to 2, impossible.