Before I had kids: PUBG. I went real hard on that game for 18 months. I played 10+ hrs a week and never lost interest.
After kids (PUBG is stressful, I don't need more of that) it'd be Rocket League. I've been playing it consistently since Day 1 and whilst I don't see myself improving much anymore, I still get a kick (ahem) out of scoring a nice goal, or a laugh at totally missing an empty net.