Most players want more customization options and aging options. A lot of the emphasis is on aging and the creation of the sims themselves along with the customization level of the clothing.

aging
In The Sims 3, sims within the game can get pregnant and have a child. The child is born as a newborn, who stays as a newborn and doesn’t age for three sim-days. When the child does age, he ages to a toddler. Afterward to a child, then teenager, then young adult, adult, and elder.
Some players want more aging options. They’d prefer that when newborns (0-11 months) age to toddlers, the toddlers (1-2) age to young children to fit the ages of three to five. Then the young children age to children (6-10). Afterward, there are pre-teens (10-13) followed by the teens (14-19), which are then followed by the young adults (20-39), the adults (40-49), the middle aged adults (50-69), and finally the elders (70+).
While some players think this many aging options is a lot, many players think it’s a great idea and would love to see it in The Sims 4.
As many players that want more aging options want some more room for customizing their sims the way they want. In the current game, the height can’t be adjusted, the hair can’t be changed, etc. Players want to change the height with sliders, along with the hair length and type.
Personally, I think they should bring The Sims 2 back a little with the sliders for clothes. There were sliders for sleeve length, for collars, for skirt, shorts, and pants length. There were sliders for the way the pants flared out, etc. There were also layers of clothing like an undershirt, a regular shirt over that, and a jacket over that if the player wanted.
Sure, The Sims 3 tried to balance the lack of customization on the type of clothes with Create-A-Style, which allows the player to change the material, color, etc. of the piece of clothing, but it hardly compares.

Landscape
Many simmers get agitated due to the fact that there are landscaping limits and rabbit holes. Rabbit holes are when a sim goes into a building, like their work building, etc., and the player can’t see them or what they’re doing. Developers are getting better with this with ever update, however.
Building a house can be fun but annoying due to the limits. Some players want to place a driveway on a hill, while others want to change the height of the walls and roofs. Landscaping options are pretty vast right now, but simmers want more. They want to manipulate how the stairs go up to the next floor and how there should be no building limit. If you want to make a massive mansion, there should be no limits.

http://www.the-sims-4.com/the-sims-4-expectations-and-predictions/