1. Better build options - different stair types, a stage tool, multi-level foundations on the same lot, sliding glass doors, better color matching of objects, being able to delete the underside of roofs leaving just the roof (similar to what we can do with stairs), curved pools, the option to remove "snap to grid" on any object, being able to color ceilings, glass walls.
2. Weather and seasons (not seasonal worlds- seasons in all worlds).
3. Less "sitcom" play and a bit more realism (everything isn't always awesome).
4. Elaborate on Sixam- I would like to see the Devs have fun with this idea and come up with a futuristic, alien world that allows my Sims to take a break from the normal everyday world in which they currently exist (an alien version of TS3's "Into The Future").
5. Expand emotions- Fear and phobias should be a part of the game.