I've played two previous animal crossing games and even the mobile version and even pocket camp.
The biggest draw to these games for me is their non-violent, wholesome gameplay. They're an excellent escape. You get to experience a place where everyone is nice and enjoys your company. But it goes deeper than that. The interactions with the animals and dialog present throughout this game is exceptional and surprising. The animals will say and do things in a way that makes them feel alive. The attention to detail in this game is amazing.
I've seen people online turn their whole islands into full cities. The customization is endless and every time you open the game there is always something to do.
I got about 2 years of gameplay out of New Leaf. I'm hoping they'll keep releasing DLC for New Horizons that will give this game many years of life.