Expansion Packs
Cats & Dogs ~ An absolute MUST for the pet lover! It's worlds above the Sims 3 Pets, as the animals actually look like cats & dogs and not giraffes. They are adorable, and the amount of detail gone in to making the pets do actual pet things is amazing. If you're not a pet lover, you could probably do without though the new world Brindleton Bay and alot of the build/buy stuff is pretty awesome.
City Living ~ This pack introduces SO much gameplay! San Myshuno is one of my favorite worlds of Sims 4 period, as the views are amazing. There's apartments, festivals, fun new careers (politician, critic and social media). You can do karaoke, graffiti (on specific boards/murals), and play video games. There's nothing I don't love about this pack.
Game Packs
Strangerville ~ I was actually hesitant about this one at first because I knew it was a Stranger Things ripoff, and I'm not a fan. But when I actually gave it a chance, I regretted not buying it sooner. I love the desert world, so much different from Oasis Springs with much more character to the surroundings. I'm BIG into conspiracy theories also, and I adore that that can be a thing thanks to this pack. You can buy conspiracy books, have a paranoid trait, and even bug people and listen to their conversations. If you hit pay dirt, you can blackmail them lol
Jungle Adventure ~ Selvadorada is a beautiful new world with much to explore! The new decor is amazing too, with a bit of a southwest feel to it. I really enjoy paying with the new archaeology skill and the skeletons are cute.
Stuff Packs
My First Pet ~ If you decide to purchase Cats & Dogs, this is a good supplemental pack (note that you can't play with some items unless you have C&D expansion). I love the tiny creatures, and they can even earn you money because they write books and blast off to space and have rave parties. The circular aquarium coffee table is also my favorite in-game object EVER. It's in every single house I play in, whether it belongs or not. I love all the build/buy and pet costumes too. Not as bad as everyone says.
Bowling Night ~ I love to watch my Sims bowl, and have the hidden skill too. The clothing and build/buy is some of my favorite stuff in Sims 4.