How do you keep it interesting?

I used to be a family player only and I would get to gen 3 and get bored but the past couple of saves I've built Newcrest from scratch and I create my main sim then add other sims in it who I want them to have relationships with (friends, lovers, enemies etc). I always have a main legacy sim but when I fancy a change I just play another household in the save. I've also experimented with play styles that I've not done before so I'm finding that I'm really enjoying my sims atm. I also sometimes nip in to premade sims saves, give them new looks and manipulate their lives ie. Make them have affairs, get them pregnant etc. I do like it when they have children because when my main legacy sim is ready to have babies then I know theres other children for them to make friends with.