I've been playing Sims 3 while waiting on new content for Sims 4. Yes the graphics and gameplay are smoother in 4 and I do prefer the asthetics of 4 over 3, but there is a lot more to do and keep busy in Sims 3. I recently went back to create a world and made my own world with all content from all packs and space for store lit content and I'm enjoying it.
If you're just looking for something to do while waiting on Sims 4 content then yes I do recommend it as it does have gameplay, like open world, that is different then Sims 4. If you do decide to invest in them then I also recommend looking for some player built world's as they often consolidate stuff from all packs.
But I do worn you the Sims 3 and Sims 3 store has not gone down in price so it could get expensive. If you are able to find compilation packs or the whole set for a decent price go for it. If not then just get one EP that interests you more than the others with the base game and give it a try before going all in.