Funs things to do with base game alone?

Challenges-wise, my personal favorite is Rags to Riches (or, I think, it also tends to be called the Rosebud challenge).
Take a Sim and move them into an empty lot, use a cheat to remove their funds and then work your way through all the possible ways of earning money to get to a "rich" status: have a decent-sized home, if desired have them find a partner and start a family, whatever you desire to be the final outcome. It's fun because you can set limits to achieve your money goal: only earn money for gardening, restrictions on the kind of job you can have (no full-time job, no job at all...).

Another fun one (that might get a little grindy though) is the Super Sim challenge: try to get your Sim to max levels in all available skills, complete all aspirations, etc.

With the CAS Stories, one thing to do is to randomize the answers and then a) build a house for the Sim that you ended up with and b) see where their starting point leads you.

But generally when it comes to playstyle, while some of my saves did start as challenges, others I've played Sims based on a TV show, then just lived out a possible story for them. With those and with any other Sims, the fun for me is in creating stories. Self!Sims are a fun way to do so, if you're so inclined, but also creating Sims and setting them goals: a family, work success, friendships, then playing to achieve those.

TS4 is quite fun for rotational play. I played about half a year with just the base game. Each player has their own rotation style. Personally I like aging on for active household only and irregular rotation schedule. Best time to rotate a family would be between 3am and 6am to minimize the risk of sims missing their work.

One mini challenge I did was (as I love gardening) , to have all the plants without cheating (it was tempting to dl from gallery at one point). I used only seed bags and the plants I found from the worlds.
I was glad I started with that hood at Oasis Springs where Johnny Zest lives, as that is the only place you can get tomatoes from wild. I got some fruits from fishing as well. Took some time but I had to finish it , only one left was orchid, if I recall right, it took forever, because I made some tiny misstakes at crafting :)

"FurSimsOfficial;c-17263287" wrote:
Maybe start of with some of the most amazing and realistic looking houses on the gallery. I am always checking on this account. There is a lot with just BASEGAME materials and sometimes.. it is unbelievable :o Super talented creator!

Link went nowhere.

I played happily since the beginning just adding in packs as they came... but I had fun for a very long time with base game stuff only (before they added in all the free stuff.. which must make it nicer). Mostly I did the suggestions already talked about here. Lots of getting to know the game... making super sims and super kids/teens. Getting through every career. Trying sims with every trait. Making super kids and trying to remember to save them to my library to make "base" sims later. I absolutely loved gardening and rags to riches kind of play. Another thing I did as a more deviant player was try to make every ghost available in the game ... I got to practice my kill them off techniques and planning that way.

I like to recommend this challenge because it's pretty easy and doesn't require too much commitment. It also let's you see your sims in a different light. Basically it's a trade off play between 2 opposite or conflicting trait sims that you play until they finish a few goals. You only get to play one sim in the household for a week before switching to the other. It's fun to see what they will or will not do on their own, what trouble they might get into... and then later as you give them more skills and direction how that might influence them when you don't play them.
https://forums.thesims.com/en_US/discussion/955171/trade-off-ts4-game-play-challenge-by-eqcreations/p1

When I first got the game, I started with the Decades Challenge. It helps give some fun parameters to the game and since I love history it was an added bonus. I helped me explore the game and appreciate each pack I added as a I played.

I also started a premades rotational save for base game characters. That was fun and helped me explore the different aspects of the game.