I must say, I love Sims 3, but the one thing I really, really miss? WEATHER!!!
I loved the snow (and the Penguins!) and the possibility of snow days, etc. Plus the category of outerwear was great fun too. I had the cutest raincoat.
I think it would be a great expansion if they did it with a "Green" theme - i.e. not just recycling, but more of a self-sufficiency thing, with more farming, animals, solar panels, composting, green houses, etc. Sort of like they did with Seasons, but more so. Soon, EA, right??