I played TS3 when it first came out and even after TS4 came out since I felt 4 was barely a proper sims game at launch. However after a few packs and the toddler update came out I decided to play it. Honestly I found 4 fun for the first time and stopped playing 3 for a few years. After many retarts I'm on my 5th generation in Sims 4 and am still not having any lag issues like I had in TS3. But I have realised that the life stages I enjoy playing (toddlers and children and teens) are missing out completely from TS4 as there is barely anything for them to do. Even with Parenthood.
I decided to reinstall TS3 a few days ago and after installing it with so many mods (new UI color, new skill gaining color and grid updates as well as heaps of gameplay mods) I am having so much fun in TS3!! Generations makes my favorite life stages so so SO fun to play. I never felt like I could do everything in TS3 because there is so much to do and I am loving TS3 again at the moment. I still feel like I have barely scratched the surface and I've been playing TS3 on and off for about 11 years now.