1. Seasons, definitely. Also rain, sandstorms for OS, and hailstorms if we ever get a snow town or in any town that would have a winter season.
2. More worlds: Medieval/Goth world, Hawaiian-themed world, and snow world as mentioned. Could make it crazier and add an Atlantis or "City in the Sky" world.
3. College/University.
4. New careers, as much as possible to keep adding diversity and more options to the game. The ones I want most are: Teachers, Magician, Fencer, Fashion Model/Designer, Paranormal Investigators, Pilots/Flight Attendants, Military, Farmers, Archaeologists/Historians, Actors, Dancers, Singers, etc.
5. New skills to accommodate the new careers (Swordplay for fencer, magic for magician, etc)
6. More vacations: cruise ship vacation, resorts, etc
7. More venues: amusement parks, zoos, dojos, beaches, etc
8. Expanding on the dojos venue and Fencer career, I'd love a martial arts skill so I can finally make a club for that, where sims can learn taekwondo, karate, jiu jitsu, etc.
9. Burglars.
10. More emotions as mentioned. Jealousy should also be one. Also, Bored is such an infrequent emotion and I feel it should be more common than that. Have low fun = Bored and add a "Very Bored."
11. More traits and also the ability to add more traits than 3 without cheating, as some people have more tend personality. Some thoughts on new traits: Paranoid, Boring, Violent, Timid, Emotional, etc.
12. The ability to choose what sexual orientations sims identify as, to help stop autonomous flirting with either only males or females. Also a choice to stop flirting/developing romantic relationships altogether for sims when they aren't single. Could be a trait (Faithful).