I barely remember past iterations. There are some things I miss (like crawling toddlers) and some things I don't (the pudding faces in Sims 3). As for Sims 4, families are more like families than they were in previous games - parents and kids can interact in much more sophisticated ways. I like being able to transfer Sims from household to household without mods, and I'm glad the requirement for eight billion friends to get a work promotion is gone. I love being able to use any category of clothing (male, female, gymwear, sleepwear) when creating outfits. (But, for the love of the Great Llama, can't we please have swatches that match? I don't want a colour wheel. I just want things to match.)
There are still things I want from S4 - some will come in expansion packs eventually, some things won't. I do feel like I can play S4 the way I want to play it more than I could the previous games (or, at least, I can do what I want to do without mods).