Being able to create patterns with transparency, the ability to decorate outside + decorate in half-grid increments, the ability to pick up trees and put them somewhere else, terraforming, island hopping for new villagers + villagers not moving without asking, etc... all of those things make New Horizons really great for those of us who like to have so much creative control over our islands.
New Leaf is just great in general, and I have so many great memories playing it with my best friend. I also loved going to the island at night to catch beetles with that PREMIUM island set up lol, and there was so much great furniture that I love and miss, like so many great food items, versatile furniture sets such as Alpine, Sloppy, and Rococo. Interactions with villagers were more fun too, even if all the delivery requests / house invites / etc. could get a bit overwhelming sometimes.
I didn't care for City Folk honestly so even though I played it, I don't have much to say.
I haven't played Wild World (weirdly) so I can't comment on that, but I've heard it was great. Unfortunately, with all that we can do in NH, I think I would get bored with it so it's a shame I didn't try it earlier.
Gamecube / Population Growing... where to even begin. I love this game. Your day would consist of delivering a watch to a villager, getting called ugly by another villager while you're just trying to vibe, having a villager let you know they painted your roof without permission, and then having them proceed to call you ungrateful when you get upset. Maybe make a mistake and reset and then have Resetti yell at you for 5 minutes before making you type out "I'm a loser." Scrubbing Gracie's car and getting an ugly shirt in return for your hard work, and yet waiting in anticipation for her next visit. Premium gameplay, 10/10, I wouldn't have changed a thing. I played this game for hours and hours as a child, sometimes I wonder what I even did all day in that game, but I loved it and it was a very important part of my childhood tbh!