I've been playing animal crossing for almost 10 years.
New Leaf differs majorly from past iterations in the fact that you are the mayor in this game. You have to unlock shops on your main street, pay for public works projects, can sign ordinances into law, and do everything else you could do in previous animal crossing games.
Animal crossing's premise is simple- you are the only human in a village full of animals. You can make money- known as bells- in order to fund public works, make your house larger, pay for new clothes, new furniture, new wall papers, new designs which you create yourself, and new tools.
The town also houses a museum, where players can donate the fish and bugs they catch, the fossils they dig up, and the art pieces they purchase. It doesn't sound like it'd be fun, but it's satisfying seeing your museum fill up with everything you've donated.
New Leaf is the most customizable game in the series. You can put custom patterns on certain furniture items, choose how you want your town to look and how you want to develop your town, and as always, create your own designs to be used as clothing, wallpaper, carpets, or pictures.
The reason I say New Leaf might not be the best starting point for newcomers is that it doesn't explain the mechanics of Animal Crossing as a whole too well. Aside from being mayor, the core of the game hasn't changed much. And for someone who's never played the series before, the additional challenge of being mayor might be overwhelming. However, New Leaf would be a good starting point for older fans (10+).
I've been playing for a month now, and in a game which is technically endless, I've hardly scratched the surface of what's possible. However, what I know is that Animal Crossing is a pleasure, but be warned that for optimal game play, it'll require an hour minimum of the player's time daily.