The 5 most important things that you need NOW !

I would be very happy if the game could include :

1. Different Eyes ( Heterochromia) : To complete my TS3 story transferred to TS4, my character used CC in TS3 but now I don't download CC anymore.
2. Zombies : To complete my TS2 story transferred to TS4, my character was an Alien -Zombie
3. Spiral Staircase : To manage better the space in duplex apartments (San Myshuno) because standard staircase is too big.
4. Drums : To complete my TS2 story transferred to TS4, it was the favorite musical instrument of my character
5. Firefighter active career : I don't like to work in The Sims but Firefighter career is one of my favorite jobs. Rescue people is never boring.

Hotels

Bands that can be scheduled to appear on lots so my non musical sims can go enjoy live music

Not to be that person but, game fixes. I want my eco lifestyle community lots to work, I want to use for rent apartments without fear of corruption, I want my sims to stop freezing up. I want the items I craft for small business lots to stop disappearing in rotational game play.

I would like another adventures style game set in Argentina with dinosaur dig sites and the ability to put the bones together to create dinosaurs and expanded museums with kids activities to house said dinosaurs

I want to create my own festival lots like in the sims 3.

I just started really building in Sims 4 and as former big Sims 3 builder—this is what I feel—I need NOW!

1. Better matching colour swatches: so many look like they might match most/other EPs but they don't, some just are missing and others don't match much. In some cases top cabinet swatches don't even match bottoms (L&D for example).
2. Spiral Stairs: I love these (as they are extremely condense) for two floor solariums, greenhouses, and Victorian builds.
3. Mirrored versions of  existing doors: some doors have unique looks on either side but the opposite is often needed.
4. Steampunk build/buy set: my favourite theme and though I can work with many items to make a passable Victorian/Industrial theme—it isn't Steampunk enough for me.
5. Debug improvements:  you cannot change light colours/dim and add plants (harvestables) in various stages without being in live mode, needed organization (of plants/harvestables, visual spawners, etc.), add missing debug items (hidden to players but used by devs), etc. As well as a way to not have to repeatedly re-enter debug cheats while building.

1. Camera overhaul. The jumping when on lots with more than one level up is super annoying and the sound is tied to the level the camera is on too. Zooming in is missing a few steps too. Makes no sense that we must hide the UI via tab to enter a secondary camera mode to go everywhere but the normal camera cant do half of that.
2. Remove CAS filter for makeup and acessiors and a few other categories. Who needs warm weather lipstick filters?!
3. New items from packs that already exist in older packs or base game but just have a different texture should not get a new slot in the build mode items list but just add to the already existing item.
4. Feature to organize the pie menu the way we want, hide options we never use and move some to a better place.
5. Fix the eco pack. Green lots and regions constantly reset to neutral even though the lots didnt change.

1. Traits doing way more than they are doing now to give Sims unique personalities.
2. Sims never doing anything they dislike out of their own free will so picking dislikes matters. 
3. Five traits like Sims 3 in character creation, 3 is too few. 
4. Sims stop obsessing over the same few objects. 
5. Way more animations for everything. This game does not have even half the amount of animations as Sims 2. 

Vechiles for moving Sims in and out the house, parents dropping kids off to and from school, parents going to work, the school bus shows up, watching your neighbors leave or come home. It will feel realistic and lively. 

Both Preteens and Middle Aged Lifestage. Sims throughout the franchise kept missing the middle stages in life and they are the most important they finally recognized infants but that's because simmers kept complaining about the baby stuck in the bassinet. However Preteens and Middle Aged are also the middle ages that kids develop into a preteen they are older then a kid but younger then a preteen and they are going through changes the start of puberty like the voice cracks, they noticed that their body developed more and their more moodier because it's the early stages they don't know how to handle puberty yet. Middle Aged Lifestage it's the end of puberty they won't have kids, early retirement, have a senior discount, still be a fun grandparent can do things without over excursion like woohoo. 

Pacifiers and Strollers All 3 need pacifiers the newborns, infants and toddlers it look cute and it will soothe them so the parents don't have to keep doing it. Strollers for both infants and toddlers, The Sims are not pack mules stop putting everything on them we put everything in the inventory, they have to carry toddlers and put infants on their backs. Toddlers are so slow I get they are learning to walk but when we go places they are incredibly slow please we need strollers also it would be fun and cute and realistic to see families walking around the neighborhood with strollers. 

Vacation to check in and out of hotels and resorts experiencing a great holiday or a jet 2 holiday. Honeymoons, family vacation, single vacation. 

1. Dragons
2. Bug fixes
3. The ability to play true historical saves without being forced to resort to modern tech
4. An Outerwear clothing category that functions by season
5. Spiral staircases

"Bug fixes" isn't a feature or gameplay that people should dream to see in a game ...

I know, but the game is so buggy I felt it had to be included.

• I long for mermaid housing and underwater gameplay. I'm hyperfocused on this single issue to be honest. But since you asked for 5...
• A European medieval town with a medieval fair, which would include the pit monster.
• The Rainbow Montain of Peru in a South American world.
• Unicorns. To me unicorns aren't horses with a horn. They're like we can sometimes see on medieval art, or in The Last Unicorn: smaller, with long hair growing at the tip of their tail, behind their leg about their deer-like hooves, and sometimes under their chin, like for a goat.
• An empty world, set in a desert, where I could build a Moroccan town, or anything that would fit the Sahara landscape. Or just give me a Moroccan world to be honest, I'll be happy either way :p