The overall variety of things you can do especially with mods like Traveller, which opens up the possibility of traveling to every world you have installed. It's like you can play this for years and never really be able to organically discover everything this game allows you to do.

The traits add so much color, personality, and variety to sims as well, mainly because they do act it out. There's a noticeable effect in their moods and how they interact with the world. I love how a Neurotic Sim really does spontaneously freak out or checks if the sink is working. An over-dramatic Sim can swoon or pass out for fun. There's just so much about it that gives depth to the game.

The story progression is also one of my favorites, especially when greatly enhanced by the Nraas mod. It makes the game feel so much more alive and real, like things are happening all around you and it's not all about your household.

Everything else I can say is tied to the open world, because that alone opens up so many possibilities for unexpected storytelling. Like how if my sim's house is close enough to the neighbor's house and there's a toddler next door, I can hear the toddler crying at night.

My Sim was taking a stroll with her toddler and saw smoke coming from a house in the neighborhood. I used nraas to open the house to see what was happening inside and the owner was freaking out by the fireplace. Watched as the fireman came to put the fire out while my Sim continued her stroll.

Another Sim I had was on a water taxi in Isla Paradiso and just observing the surroundings, I found a ghost boating in the middle of the ocean. It's those things that make the experience full and unique and memorable. I can ramble on, but yes. Those are some of the things I love about TS3.