1) Island Living needs a rehaul. At the very least its mermaids need some kind of skill tree to match most of the other occults, and I agree with a lot of others that the addition of at least one underwater lot in that world would be liven up a trip to the dive buoys. (Perhaps a hidden lot that only mermaids can visit?) The off-lot space in Sulani needs more objects to make the corners of the map worth visiting.
2) Outdoor Retreat needs to allow for bugs outside of Granite Falls, and just have more to do - for all the family - in that world. It's such a boring world for toddler, child and occasionally elder sims. Why can't the toddlers catch - and eat - uncooked bugs? Swimming would be wonderful, but I'd like to see an overhaul to the hiking now along the SE style, and more family/interactive play between sims.
3) Seasons needs something new added to it, because most of its main draw/unique features have been stripped out and reused now in other packs like Spooky Stuff and Snowy Escape. Maybe the ability to ice-fish in winter. Snow depth? I keep completely missing the fact there's a blizzard outside my sims' home because it looks exactly the same as it does every other day in winter in-game. I'd like to see my sims at least partially snowed-in. Every now and then during a summer heatwave, a water limit per day is randomly imposed for a few days.
Honourable mentions for minor touch-ups to:
Get Famous, imo, mostly needs an expansion in which careers automatically grant you fame as you ascend in their ranks. My entertainer and celebrity chef sims should not be struggling to stay famous when they go to work, or relying on chance cards.
Dine Out works fairly okay in my game, but the meals need to sped up dramatically.
Realm of Magic just feels a little lacking? I've only had this game a little while and haven't done much with it yet, but the actual RoM just feels a little sparse. Also some spells/buffs/whatever that make it a little easier to play - and be acknowledged by other sims in-game! - as being an evil spellcaster. Because, sure, I can tell MYSELF that my sim spellcaster is evil and has the evil trait and everything, but there's not much ability to differentiate between them and the 'good' spellcasters.