IMHO, Sims 3 still looks... more real. Gameplay graphics comparison is like Sims 4 is akin to Team Fortress 2, cartoony with waiting in between all the game play. Sims 3, like a Grand Theft Auto game, where realism was the art style, and you can go anywhere in the world without loading, even switch between areas in the game where different sims are doing different things.
Sims 4 has almost been out as long as Sims 3 was when they stopped putting out content for it. Yet Sims 3 has WAY more content I like.
In sims 4, your sims that are not the active household are more used as props, or extras, that can be on any and every set or scene, just to make it seem busy, with traits that are shallow and have little to make different sims actually behave differently. In comparison Sims in 3, have more traits, that have a bigger behavioral impact, that effect where they go when they are actually not busy, because yes, they live their own little lives just like your sim.
I could be wrong, but I feel like Sims 4 at this point, has the least content still of any sim game.
TLDR, My opnion is an unpopular one, but yes, you should certainly give Sims 3 a shot. If you want more enticing posts from people who play it, check out the Sims 3 area of the forums, where I'm surprised this post didn't already get moved to, that used to be the thing.