This are just my personal opinions from playing the Sims franchise and recently giving 4 another try. I bought Sims 4 the first month it was out, so it was just the base game at that point, the Game packs and Stuff packs weren't out yet. I got pretty bored within a few hours of actual gameplay.
I've loved each one of the Sims incarnations, each brought something great to the franchise. Sims 4 has a amazing CAS, I can easily sculpt certain facial features, and I don't need a bunch of sliders to achieve different and varied looks in Sims. I can spend a hour or 2 in CAS, tweaking and changing my Sims before I load a world. But, a majority of the gameplay for me just feels flat. The game seems a bit more linear than the previous games. I feel the base game was almost built around people needing some DLC in order to liven up the game. I know expansions and DLC always made 1,2 and 3 better, but I didn't feel like those games were bare bones without Vacation or Seasons.
I'm disappointed with the personality traits, I feel like Sims 2 and 3 did it better. I'm hoping that they add a Hot Date, or similar expansion to introduce a nice romance mechanic. The game feels a bit incomplete without any sort of attraction, or turn ons and offs.
Sims 4 does seem to be built with modding in mind, I notice there are a lot more mods, and huge overhauls like Pre K and College. Things that came out very late into the lifespan of Sims 3, or not at all.
The things that Sims 4 did better, just doesn't stack up (for me), to the previous games. It feels in many ways like stepping backwards in the franchise. I really wanted to fall in love with this game, like I did with the past ones, but I still find myself getting bored very easily.