Can I share two small things that I loved in TS3 that I really want to see in TS4?
1) recipes! I thought it was so much fun having to learn recipes, and collecting new ones from all over the world. I loved that you had to have a certain cooking skill level to be able to learn the more difficult recipes. It made cooking so much fun. I think cooking in TS4 is already great, espeically with the animations and all.. but adding the recipe element will make it 10x better.
2) this is tiny... but I loved how, when you picked flowers in TS3 you could drag and drop the flowers into the world and it would automatically be in a pretty little vase for display. There are so many flowers in TS, I just wish I could display them!