I still really enjoy all the City Living Festivals, my favourites are Humour and Hijinks and Spice Festival. Island Living Festival I rarely participate but feel they're okay, kind of cosy. In Snowy Escape I've visited Festival of Lights and Festival of Snow many times, but I don't like Festival of Youth (only visited once though). Are Cottage Living competitions counted as festivals? Those are pretty boring, but I also want to compete so I take it. Overall festivals have gotten worse, there's just less to do. I like having them, but feel they could be better.
My best tip is to edit the locale where your sims travel during the festival and make it interesting, so that if the festival bores you you can spend some quality time there. Personally I always stay until the end of the festivals because I don't want them to overlap - I don't know if that's still an issue? At the end my sims will sometimes be napping on the benches because of this.