TS4 toddlers are GOAT (greatest of all-time) I say this as someone who played all the games in the franchise, with TS3 being my all-time fave. The devs did toddlers so well and really brought life to them. Next to YA, they are most fleshed out life stage in the game. I love them so much.
Holidays/Calendar. I love this. As someone who never celebrated holidays, birthdays, etc, it's great that I can customize my own "holidays". Since I don't observe Christmas and things like that, my Sims don't either. I have made all types of celebrations for my Simmies, some with cultural elements like Blacktivus, that all my Sims observe no matter their ethnicity or race. The newest holiday I created is called Lokahi Festival which is the "Harmony Festival" that is native to Sulani. It's a real Hawaiian word, and I just used to make a two day celebration that native and non native Sulanians observe out of respect for the culture. They dance, eat, enjoy spending time with their neighbors and loved ones, etc. It's very community based because that is how my Sulani is. I didn't approach it like a vaca world. All of the Sims with the exception of my mermaids, I created are Sulani natives to expand on the living and cultural aspect of the world. They operate very differently than my Sims who live elsewhere. have around 120 active Sims I have created. I don't play all of them, but I play most because many live on apartment complexes or multiple house lots. I think the devs did a good job with at least making Sulani feel contained as opposed to other worlds, at least that is how I see it. There is not as much gameplay as I would have hoped for, so I have had as I so often do in TS4, come up with workarounds to add more realism and depth to my game.
Clubs are great. I like how they expanded on this feature from the previous iteration. I love making clubs that are focused on shared interests between Sims. I have so many different clubs and I want to make more as time goes on.
TS4 also has better fashion choices for male Sims. In TS3 the clothes left much to be desired and I used a lot more cc because of this. I still use cc in TS4, but I am so happy that my fellas at least have some nice options from the game itself. TS4 furniture and amount of objects like clutter and styles of furniture is great too. I love that they added things that make a house feel more home-like. If there was a stuff pack with just clutter, curtains, and rugs, I would be happy. LOL