If it wasn't for how easily the Sims 2 corrupts without mods I'd say it's better in literally every way. Even with only 5 0-10 personality sliders it gives them more traits than actual traits, like a 0 nice Sim would oh so be mean-spirited but it actually allows balances you can't get with traits. A sim that sometimes cleans up? Possible. A sim that never cleans up? Still there. A sim that cleans up enough to be sanitary? Also there! Traits always should have been additions to their personality like vegeterianism. Not 33% of their actual personality
Hobby enthusiam and turn on/offs also add more personality than traits ever would. Sims show their love for somethings and get proper rewards for it as well as small idle animations and chatter with Sims. (you wouldn't catch your sims who love science at a computer for too long when they have some sciency things to do) Turn ons make attraction actually have options and possible challenges, if a Sim doesn't like black hair then it'll sure be hard for people with black hair to get their attraction.
TS3/4 have this issue where traits are just one side of each personality spectrum turned into traits as well as what already was there as aspirations (family oriented is literally just the family aspiration)
Whims are just wants with no substance, instead of it being something big for their life like your teens wanting to go to college, pleasure sims wanting to go have perfect date and friendly sims wanting to be friendly and make BFFS, TS4 just makes whims super minor basic things that wouldn't affect anyones life much. TS2's fears are a nice extra dimenson of personality (which they also involve). Sims who've peed themselves often fear doing that again, Sims who made enemies want to actually apologise and fear the thought of being insulted or if they're mean, just win fights and would fear the thought of losing said fight. Extremely neat sims fear the idea of using public toilets and how dirty they are but a slob just woiuldn't be afraid. Same for wants, they're often led up from what's happened recently, my newly wed family Sims often want nothing but to woohoo for a good day with their spouse. My knowledge Sims would want to become occults from their time spent with occults and Romance Sims just want to woohoo that townie they fell in love with and kissed.
Oh and interests, like with enthusiam, these link in nicely, minor things your Sims (and pets!) talk about, someone might hate talking about money but over time talking to others and reading about it they could grow a new interest which they'll bring up in casual chat and their thoughts. They even have nice animations and dialogue for it, makes them really seem lively and have some character to them
It has custom music per station so it's easier to have custom music without mismatches and custom TV channel videos so you can grab a bunch of video files and put them in and watch your Sims watch them. Custom paintings are fun, my houses have a ton of them all the time since I can easily drag/drop a PNG file or one hundred.
Occult hybrids are fun, and it has proper plantsims. Picture how sad it was seeing plantsims being both sims that are tempoarily green and witches that cannot become vampires. Plus it adds challenges, like try a alien plantsim vampire werewolf and you'll have a rough time, but it's ultra fun. Or bigfoot witches and zombie vampire servos. Hybrids are fun.
Memories. Now, memories are exactly what they should have been. Sims can feel down for a week after an event like peeing themselves at a party and can talk about it for the rest of their life a little more casually, but they won't DIE OVER IT and only feel very sad about it for one day (or one object changing their emotions) plus it's fun to build up a huge list of memories and check them out to see how their life has went whether good or bad.
I could spend all day eviscerating the Sims 4 with criticism but I'll spare that game. For now.
Also it has Bigfoot, and I like bigfoot.