As TS3 is a new experience why not fully explore the features which were new to this version. After playing TS2 you already know how to mix and match the packs to give your sims the best possible experience but with TS3 you also get some gorgeous open worlds for your sims to live in. These can be fully explored, deliberately or by sending your sims out to collect gems, metals, seeds etc. You also have the ability to garden and fish, swim in the ocean and with IP deep dive (mind the sharks :D ).
Personal favourite fun things - making snow angels, using the tanning booth, ice skating, flying a broomstick, having a dorm party, the architect career.
The other thing to remember is there is so much (particularly when you add store content and cc) that it is impossible to enjoy it all in one go. Better to select a few things to try at a time and go back to what you like best.