Long read ahead
You're the mayor, so you can develop the town. And by that I mean, Public work projects which allows you to build new things in town like a bench, waterfall etc.
And ordinances like changing the time shops open or make flowers bloom without the need to water them everyday.
You can change the outer of your home, which is really nice, and you can hang stuff on walls too, like clocks, you can buy houses and furniture from nook's homes.
And his brother I think sells tools.
Plus there are many shops now, like club lol where kk is a dj, kicks, where you can buy socks and shoes, you can wear shorts too.
And a plants shop which is nice, and oh, a photo booth. Do you think your character looks will be according to your mii?
There's an island (Tortimer) which has it's own currency and it's summer all the time there, you can go there with friends. The Online play here is exciting, to visit other homes you gotta build a place where you can dream.
I heard that if you can't find your animal friends, you can call the friend's name in the microphone and they'll show you where he/she is. And there's a map on the touch screen finally, no need to go to the map every time like in the ds version.
Finally in the Coffee shop YOU can serve customers, nice. And if you make them happy they'll give you a gift.
You can swim, ahhh, relaxing.
And there's a medal system, if you do certain things you earn medals, like in BW 2.
Oh, the clothes designing, you can save them into QR codes, YAY!
There's streetpass, I think you figured out what you can do with it so, no need to explain.
In the museum, you can finally create your own exhibits.
There's a place called DIY design where you have furniture made from Cyrus, he'll take your furniture and put a new look to them also.
In the place where there are shops and stuff, there's a store called the general store where you can buy all sorts of things, like fortune cookies, and one costs 2 play coins. Yes, play coins come to play in this game.
Wow, so excited yo.