There are so many missed great opportunities in some of these packs when you really think about it. It's hard to pick just one for some of them, but I'll give it a go...
EP
Get to Work: Active Firefighter career and NPC
Get Together: More dance styles including couple dances
City Living: Singer career
Cats & Dogs: Dog shows/competitions
Seasons: Option for teens/child sims to go trick or treating solo, with parents or as a group
Get Famous: Film director career
Island Living: Underwater gameplay (I want hotels/holiday homes too - hopefully they will still come in another pack)
GP
Outdoor Retreat: Option for sims to walk/hike together as a couple/group (I want werewolves so much, but in a new pack)
Spa Day: Option to own/work at spa
Dine Out: Option to propose at table
Vampires: Vampire hunters
Parenthood: Caregivers can sing lullabies to toddlers/child sims to help them sleep (or some other cute interaction like child/toddler sims cuddling their parents in bed after a nightmare, or learning to cook/bake together...)
Jungle Adventure: Bonehilda
StrangerVille: I want to be able to place photos on surfaces like the one in the trailer
SP
Luxury Party Stuff: Painted nails
Perfect Patio Stuff: More grill recipes
Cool Kitchen Stuff: Toasters
Spooky Stuff: Zombies
Movie Hangout Stuff: Cinema venue
Romantic Garden Stuff: Harp instrument (I'm hoping for a Romance GP to bring back slow dancing and cuddling in bed etc.)
Kids Room Stuff: Bunk beds
Backyard Stuff: Pool games
Vintage Glamour Stuff: Retro dial phones
Bowling Night Stuff: New arcade machine
Fitness Stuff: Dumbbells and exercise bikes (Okay, that's two, but I want them both so much and was so disappointed they weren't included)
Toddler Stuff: Prams/buggies (Hoping for this with a baby update patch)
Laundry Day Stuff: Under counter washers/dryers
My First Pet Stuff: Rabbits